Liquid crystal display device

ABSTRACT

A liquid crystal display device is provided which has a pair of substrates and a liquid crystal layer sandwiched between the pair of substrates, in which liquid crystal molecules are vertically aligned with respect to the substrates when no voltage is applied between the substrates and the liquid crystal molecules tilt in a plurality of directions to be almost parallel to the substrates by applying a voltage between the substrates. In the liquid crystal layer, when the voltage is applied, a proportion of a region where the liquid crystal molecules tilt in a direction of 0 degrees to 180 degrees is different from a proportion of a region where the liquid crystal molecules tilt in a direction of 180 degrees to 360 degrees with the angle being defined counterclockwise with the right direction on a screen being 0 degrees.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of Ser. No. 10/109,446,filed Mar. 28, 2002, which is based upon and claims priority of JapanesePatent Application No. 2001-316040, filed on Oct. 12, 2001, the contentsbeing incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a liquid crystal display device.

2. Description of the Related Art

In recent years, liquid crystal display devices have been broadly usedin various applications taking advantage of their thin-profile and lightweight, low voltage drive, low power consumption and so on. Displaycharacteristics comparable to those of CRT are realized in the liquidcrystal display devices, so that they have been used for applicationsuch as monitors and televisions for which CRTs are conventionallymainly used.

The liquid crystal display devices have been improved in terms ofupsizing, gray-scale display, and high contrast to be used as monitorsof computers or image display devices of televisions. In suchapplications, it is necessary that the liquid crystal display device canbe viewed from any direction.

As a technology for realizing this wide viewing angle, an MVA(Multi-domain Vertical Alignment) mode liquid crystal display device isproposed from Fujitsu Co., Ltd.

A configuration of a basic principle of the MVA-mode liquid crystaldisplay device is shown in FIGS. 2A and 2B. FIG. 2A shows the liquidcrystal display device where no voltage is applied between substrates201 and 202, and FIG. 2B shows the liquid crystal display device where avoltage is applied between the substrates 201 and 202. The substrate 201is provided with protrusions 203, and the substrate 202 is provided witha protrusion 204. In FIG. 2A, liquid crystal molecules 212 arevertically aligned, and liquid crystal molecules 211 near theprotrusions 203 and 204 are aligned with a tilt. In FIG. 2B, liquidcrystal molecules 221 are aligned in accordance with the direction ofelectric fields. In other words, the liquid crystal molecules arevertically aligned where no voltage is applied thereto, and when avoltage is applied, the liquid crystal molecules tilt in four directionsseparately in four regions respectively. As a result of mixture ofvisual angle characteristics in the respective regions, a wide viewingangle can be obtained.

Fujitsu Co., Ltd. applied for the technology of further improving thevisual angle characteristics of the MVA-mode liquid crystal displaydevice (for example, Japanese Patent Laid-Open No. Hei 10-153782), andthe technology of improving the display brightness (Japanese PatentApplication No. 2001-106283).

It is desired to realize a wider viewing angle in the liquid crystaldisplay device. Further, a liquid crystal display device with highbrightness is desired. Furthermore, a liquid crystal display devicehaving both a wide viewing angle and high brightness is desired.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a liquid crystaldisplay device which realizes a wide viewing angle and/or highbrightness.

According to an aspect of the invention, a liquid crystal display deviceis provided which has a pair of substrates and a liquid crystal layersandwiched between the pair of substrates, in which liquid crystalmolecules are vertically aligned with respect to the substrates when novoltage is applied between the substrates and the liquid crystalmolecules tilt in a plurality of directions to be almost parallel to thesubstrates by applying a voltage between the substrates. In the liquidcrystal layer, when the voltage is applied, a proportion of a regionwhere the liquid crystal molecules tilt in a direction of 0 degrees to180 degrees is different from a proportion of a region where the liquidcrystal molecules tilt in a direction of 180 degrees to 360 degrees withthe angle being defined counterclockwise with the right direction on ascreen being 0 degrees.

The proportions of the region where liquid crystal molecules tilt in adirection of 0 degrees to 180 degrees and the region where liquidcrystal molecules tilt in a direction of 180 degrees to 360 degrees aremade different to be appropriate proportions, which makes it possible toperform a suitable display even if a screen is viewed from the top orthe bottom direction.

According to another aspect of the invention, a liquid crystal displaydevice is provided which has: a first and a second substrate; a liquidcrystal layer sandwiched between the first and second substrates, inwhich liquid crystal molecules are vertically aligned with respect tothe first and second substrates in a state where no voltage is appliedbetween the first and second substrates; thin film transistors eachprovided on the first substrate and including a gate, a source, and adrain; gate lines each connected to the gate of the thin filmtransistor; data lines each connected to the source of the thin filmtransistor; and pixel electrodes each in a comb or a slit shapeconnected to the drain of the thin film transistor, directions of combteeth thereof, near the gate line, extending toward the gate line anddirections of comb teeth thereof, near the data line, extending towardthe data line.

The shape of the pixel electrode is formed in accordance with the gateline and the data line, which allows the alignment directions of theliquid crystal molecules by the pixel electrode to match the alignmentdirections of the liquid crystal molecules by the gate line and the dataline.

According to still another aspect of the invention, a liquid crystaldisplay device is provided which has: a pair of polarizing layers havingabsorption axes perpendicular to each other; a half wave plate having aretardation of half wavelength sandwiched between the pair of polarizinglayers; and a liquid crystal layer sandwiched between the pair ofpolarizing layers and having liquid crystal molecules capable of beingvertically aligned.

The half wave plate, in which a film having a retardation of halfwavelength is laminated, has a retardation ((nx+ny)/2−nz)×d in adirection perpendicular to a film surface thereof (where nz is arefractive index in a direction perpendicular to the film surface, nx isa refractive index in a direction parallel to an optical axis of thefilm, ny is a refractive index in a film in-plane directionperpendicular to the optical axis of the film, and d is a thickness ofthe film) of 0 or ±20 nm or less, and the optical axis of the film areparallel or perpendicular to the absorption axis of the adjacentpolarizing layer or, in which two films having a retardation of halfwavelength are laminated, has values (nx−nz)/(nx−ny) of the two films of0.5 or less and 0.5 or more respectively, where nz is a refractive indexin a direction perpendicular to the film surface, nx is a refractiveindex in a direction parallel to the optical axis of the film, and ny isa refractive index in a film in-plane direction perpendicular to theoptical axis of the film, and the optical axes of the two films areparallel to each other and parallel or perpendicular to the absorptionaxis of the adjacent polarizing layer.

The half wave plate is provided between the pair of polarizing layers,which enables realization of a liquid crystal display device with a wideviewing angle and high brightness.

According to yet another aspect of the invention, a liquid crystaldisplay device is provided which has: a first and a second polarizingplate; a liquid crystal layer sandwiched between the first and secondpolarizing plates and having liquid crystal molecules capable of beingvertically aligned; and a retardation film having a retardation in aplane sandwiched between the first and second polarizing plates,provided such that an optical axis thereof is perpendicular to anabsorption axis of an adjacent polarizing plate, and having arelationship of refractive indexes nx>nz>=ny (where nx is a refractiveindex in a direction of the optical axis, ny is a refractive index in anin-plane direction perpendicular to nx, and nz is a refractive index ina direction perpendicular to the plane).

A predetermined retardation film is provided between the first andsecond polarizing plates, which enables realization of a liquid crystaldisplay device with a wide viewing angle and high brightness.

According to another aspect of the invention, a liquid crystal displaydevice is provided which has: a cholesteric liquid crystal layer; aquarter wave plate; a backlight for supplying light; and a liquidcrystal panel having liquid crystal molecules capable of being aligned.The cholesteric liquid crystal layer and the quarter wave plate aresandwiched between the backlight and the liquid crystal panel, andalignment directions of liquid crystal molecules of the liquid crystalpanel and an optical axis of the quarter wave plate are perpendicular toeach other.

The alignment directions of the liquid crystal molecules of the liquidcrystal panel and the optical axis of the quarter wave plate arearranged perpendicular to each other, which can prevent coloring of thedisplay screen even if it is viewed at an incline angle.

According to another aspect of the invention, a liquid crystal displaydevice is provided which has: a liquid crystal panel in which a liquidcrystal sealed between a pair of substrates; a pair of polarizingelements arranged on both sides of the liquid crystal panel such thatabsorption axes thereof are perpendicular to each other; and a domaincontrol means including a periodical pattern of any of or a combinationof a projection, a depression or a slit provided in an electrode, on asurface of at least one of the pair of substrates constituting theliquid crystal panel, for controlling alignment of liquid crystalmolecules in the liquid crystal panel. Alignment directions of theliquid crystal molecules by the periodically disposed domain controlmeans include directions to form angles of 45 degrees with theabsorption axes of the polarizing elements and another direction, andthe liquid crystal molecules are aligned almost perpendicular to thesubstrates when no voltage is applied thereto and the liquid crystalmolecules are tilted by the domain control means in a plurality ofdirections in each pixel when a voltage is applied thereto.

By virtue of the domain control means, the alignment directions of theliquid crystal molecules include the directions to form angles of 45degrees with the absorption axes of polarizing elements and anotherdirection, which enables a display with high brightness.

According to another aspect of the invention, a liquid crystal displaydevice is provided which has: two substrates having substrate surfacessubjected to vertical alignment processing; a negative type liquidcrystal sandwiched between the substrates; and a domain control meansfor conducting control to provide a plurality of liquid crystal domaindirections in each pixel including a first domain control means,provided in a part of the pixel or a peripheral region thereof, forvarying an alignment direction of the liquid crystal in a range of 90degrees to 180 degrees across a center of the partially provided domaincontrol means, and a second domain control means for varying thealignment direction of the liquid crystal in a range of 0 degrees to 90degrees.

Both the first and second domain control means are provided, whichimproves controllability of the alignment of the liquid crystal in theentire pixel.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are views showing patterns of a pixel electrodeaccording to a first embodiment of the present invention;

FIGS. 2A and 2B are perspective views showing a basic configuration ofan MVA-mode liquid crystal display device;

FIG. 3 is a view showing visual angle characteristics of the contrastbetween black and white of the MVA-mode liquid crystal display device;

FIGS. 4A to 4C are views for explaining the reason of occurrence of aphenomenon that a display surface becomes whitish and the principlethereof;

FIGS. 5A and 5B are views showing the transmitted light amount-appliedvoltage characteristics;

FIGS. 6A and 6B are views showing patterns of the pixel electrode;

FIG. 7 is a view showing a contact region for connecting the pixelelectrode and a subsidiary capacitor;

FIGS. 8A and 8B are views showing a basic configuration of the liquidcrystal display device;

FIG. 9 is a view showing a contact region for connecting the pixelelectrode and a TFT;

FIG. 10 is a cross-sectional view of the TFT;

FIG. 11 is a cross-sectional view of the liquid crystal display device;

FIG. 12A is a plane view of the liquid crystal display device, and FIG.12B is a cross-sectional view of the liquid crystal display device;

FIGS. 13A and 13C are views showing patterns of the pixel electrodes,and FIG. 13B is a cross-sectional view of a TFT substrate;

FIG. 14 is a view showing a four-domain MVA-mode liquid crystal displaydevice;

FIG. 15 is a view showing a technique of aligning liquid crystalmolecules by providing a slit in a shape of the letter Y on an oppositesubstrate;

FIG. 16 is a view showing a liquid crystal display device according to asecond embodiment of the invention;

FIGS. 17A and 17B are views showing the principle and configuration ofliquid crystal molecules tilting when fine slits are provided;

FIG. 18 is a view for explaining an example in which the open angle ofthe letter Y of the pixel electrode is changed;

FIGS. 19A to 19C are views for explaining modifications of the fineslits;

FIGS. 20A and 20B are views for explaining effects of the pixelelectrode having a tapered shape;

FIGS. 21A and 21B are a plane view and a cross-sectional view of aliquid crystal display device utilizing an oblique electric field from aCs line;

FIG. 22 is a plane view of another liquid crystal display device;

FIG. 23A is a view showing a configuration in which the electrode isobliquely formed, and FIG. 23B is a view showing a configurationutilizing the oblique electric field from the Cs line;

FIG. 24 is a view showing a liquid crystal display device employingquarter wave plates;

FIG. 25A is a plane view of the liquid crystal display device, FIG. 25Bis a view showing a distribution of the amount of transmitted light inthe case of employing no quarter wave plate, and FIG. 25C is a viewshowing a distribution of the amount of transmitted light in the case ofemploying the quarter wave plates;

FIG. 26 is a view showing a film configuration for realizing a wideviewing angle;

FIG. 27 is a view showing a film configuration for realizing highbrightness;

FIGS. 28A and 28B are views showing a film configuration andcharacteristics according to a third embodiment of the invention;

FIGS. 29A and 29B are views showing a film configuration andcharacteristics according to the embodiment;

FIGS. 30A and 30B are views showing a film configuration andcharacteristics according to the embodiment;

FIGS. 31A and 31B are views showing a film configuration andcharacteristics according to the embodiment;

FIG. 32 is a view showing visual angle characteristics;

FIG. 33 is a view showing a film configuration;

FIG. 34 is a view showing a film configuration according to a fourthembodiment of the invention;

FIG. 35 is a view showing another film configuration;

FIG. 36 is a view showing another film configuration;

FIG. 37 is a view showing a two-domain liquid crystal display device;

FIGS. 38A to 38C are views showing a problem of the two-domainalignment;

FIG. 39 is a plane view showing a liquid crystal display deviceaccording to a fifth embodiment of the invention;

FIGS. 40A and 40B are views for explaining the quarter wave plate;

FIGS. 41A and 41B are cross-sectional views of the liquid crystaldisplay device of the embodiment;

FIG. 42 is a view showing a configuration in which a scattering layer isadded to a film;

FIG. 43 is a view showing the measured result of coloring when adisplay, which is in a white display at the front, is viewed from anoblique direction.

FIGS. 44A and 44B are views showing an IPS-mode liquid crystal displaydevice;

FIGS. 45A and 45B are views showing an electrode configuration of theMVA-mode liquid crystal display device;

FIGS. 46A to 46D are views showing alignment of liquid crystalmolecules;

FIG. 47 is a view showing an electrode configuration of four domains;

FIG. 48 is a view showing a film configuration;

FIGS. 49A to 49C are views showing configurations of the pixelelectrode;

FIGS. 50A to 50D are views showing alignment controls by a protrusionand a slit;

FIGS. 51A to 51C are views showing alignment controls by an auxiliaryprotrusion and an auxiliary slit;

FIGS. 52A and 52B are views showing alignment controls by fine slits;

FIG. 53 is a view showing an alignment control by a protrusion in across pattern;

FIG. 54 is a view showing a layout of the liquid crystal display device;

FIG. 55 is a view showing a layout of the liquid crystal display device;

FIG. 56 is a view showing a layout of the liquid crystal display device;

FIG. 57 is a view showing a layout of the liquid crystal display device;

FIG. 58 is a view showing a layout of the liquid crystal display device;

FIG. 59 is a view showing a layout of the liquid crystal display device;

FIG. 60 is a view showing a layout of the liquid crystal display device;

FIG. 61 is a view showing a layout of the liquid crystal display device;

FIG. 62 is a view showing a layout of the liquid crystal display device;

FIG. 63 is a view showing a layout of the liquid crystal display device;

FIG. 64 is a view showing a layout of the liquid crystal display device;

FIG. 65 is a view showing a layout of the liquid crystal display device;

FIG. 66 is a view showing a layout of the liquid crystal display device;

FIG. 67 is a view showing a layout of the liquid crystal display device;

FIG. 68 is a view showing a layout of the liquid crystal display device;and

FIG. 69 is a view showing a layout of the protrusions.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment

FIG. 3 shows visual characteristics of the contrast between black andwhite of an MVA-mode liquid crystal display device (LCD). As forindication of angles on a circumference of a circle in FIG. 3, 0°indicates the right, 90° the top, 180° the left, and 270° the bottom.The horizontal and vertical axes indicate an angle inclined from adisplay surface with its center indicating 0 degrees. A black and whiteviewing angle of a contrast 10 (CR=10) or more is achieved at visualangles in the top and bottom and right and left directions even at aninclined angle of 80 degrees.

When a halftone is displayed, however, a phenomenon is observed in whichwhile a normal display is viewed from the front, the whole surfacebecomes whitish with a lowered contrast when viewed at a visual angle inthe bottom direction. We discovered that the phenomenon of becomingwhitish is peculiar to the MVA-mode or a vertical alignment-mode panel,or a multi-domain type panel.

Explanation is made with reference to FIGS. 4A to 4C. FIG. 4A is a viewof the display surface observed from the front. A case in which a liquidcrystal display device 400 is divided into four domains 401 to 404 isexplained. In a state that no light leaks because no voltage is appliedor liquid crystal are almost vertically aligned, light leakage in blackis considerably little even at an inclined visual angle. In the domains401, 402, 403, and 404, liquid crystal molecules A1, A2, B1 and B2 tiltin different directions respectively. The liquid crystal molecules A1,A2, B1 and B2 are almost vertical and have a low birefringence within alow voltage range.

FIG. 4B is a view of the display surface observed from this side (at avisual angle in the bottom direction). The liquid crystal moleculessubstantially lie at an inclined visual angle. Because the liquidcrystal molecules form a slight angle with a polarizing plate, abirefringence occurs to cause light leakage.

In FIG. 4C, the horizontal axis indicates an applied voltage and thevertical axis indicates the amount of transmitted light. Acharacteristic line 411 shows characteristics when the display surfaceis observed from the front as shown in FIG. 4A. A characteristic line412A shows characteristics of the liquid crystal molecules B1 and B2when observed from this side as shown in FIG. 4B. A characteristic line412B shows characteristics of the liquid crystal molecules A1 and A2when observed from this side as shown in FIG. 4B.

When a dark gray-scale is displayed with the voltage slightly exceedingthe threshold value, the amount of transmitted light increases as shownin FIG. 4C. This is because projection axes out of axes of the tiltedliquid crystal molecules deviate from a projection axis of thepolarizing plate as shown in FIG. 4B. This phenomenon occurs in the samemanner in either the liquid crystal molecules located in an upper halfpart of a pixel or the liquid crystal molecules located in a lower halfpart of the pixel. Here, a case is considered in which some opticalsubstance is inserted therein to correct the light leakage. In thiscase, it is possible to compensate a dark halftone but, on the otherhand, unintended optical effects may be produced when a black display isperformed. This may produce black floating at an inclined visual angle,which narrows its good contrast visual angle range.

The aforementioned problem is solved by basically breaking the ratiobetween a region where the liquid crystal molecules tilt in the upper(including the top right and the top left) direction and a region wherethe liquid crystal molecules tilt in the lower (including the bottomright and the bottom left) direction.

FIG. 5A shows the transmitted light amount-applied voltage (T-V)characteristics when the ratio is 1:1 between the regions of the liquidcrystal molecules A1 and A2 and the regions of the liquid crystalmolecules B1 and B2. In this case, the characteristic line loses itsshape, and the display surface becomes whitish.

FIG. 5B shows the T-V characteristics when the ratio between the regionsof the liquid crystal molecules A1 and A2 and the regions of the liquidcrystal molecules B1 and B2 is adjusted to an appropriate value. Theamount of transmitted light is almost proportional to the appliedvoltage to allow a suitable display.

FIGS. 6A and 6B show a configuration when alignment control is conductedby fine slits. In FIG. 6A, the configuration is made for all the liquidcrystal molecules to tilt in a lower direction on a screen. One pixelregion 103 is divided into two alignment regions 101 and 102. The pixelregion 103 is provided corresponding to a gate line 114 and a data line113. The pixel region 103 is constituted of an ITO (indium tin oxide)transparent electrode 111. The transparent electrode 111 is providedwith a contact region 112 for connecting to a drain of a thin filmtransistor (TFT). The ratio between the alignment regions 101 and 102 is1:1. In FIG. 6B, the ratio is set to 1:1 between a region 121 where theliquid crystal molecules tilt in the upper direction and a region 122where the liquid crystal molecules tilt in the lower direction. Thealignment in the regions 121 and 122 is controllable by the direction ofslits of a transparent electrode 123.

In FIG. 1A, the shape of a transparent electrode 133 is changed, inwhich the ratio is set to 1:3 between a region 131 where the liquidcrystal molecules tilt in the upper direction and a region 132 where theliquid crystal molecules tilt in the lower direction. Thus, as for thedirections of the liquid crystal molecules tilting, the ratio of theregions is normally set to 1:1 but is, with their balance intentionallybroken, set to 1:X (X<>1).

When the balance is broken as above, the ratio in superimposing the T-Vcharacteristics at the visual angle in the top direction on those at thevisual angle in the bottom direction shown in FIG. 4C is changed as aresult. In this event, the T-V characteristics are the sum of the twoT-V characteristic lines 412A and 412B shown in FIG. 4C corresponding tothe aforesaid ratio. Here, in the case where the region shown by thecharacteristic line 412A in FIG. 4C is increased, while its blackishimage becomes entirely whitish, the black and white contrast isbalanced, so that an excellent display is achieved by virtue of thecontrast. On the other hand, in the case where the region shown by thecharacteristic line 412B is increased, its blackish image is entirelyfilled in black and can be partially inverted. The blackish image,however, does not become whitish but still remains black. In the casewhere the effect of the characteristic line 412A and the effect of thecharacteristic line 412B are completely mixed 1:1, both excellentcharacteristics are cancelled each other, which makes it difficult toachieve excellent visual angle characteristics. It was found that,however, an excellent display can be attained by adjusting the ratio,especially by setting the proportion of the region of the characteristicline 412A to 70%±20% of the whole.

FIGS. 6A and 6B are explained in more detail. It should be noted thatdescription is made with “gridiron shape” being regarded the same as“comb shape” in this specification. FIG. 6A shows an example in whichall the liquid crystal molecules are aligned downward. The transparentelectrode formed on the TFT substrate is patterned. The transparentelectrode 111 is provided in a comb shape here. The pixel is dividedhere into the two regions 101 and 102, in which teeth of the comb areset to extend to the bottom right in the upper half part. On the otherhand, teeth of the comb are set to extend to the bottom left in thelower half part. Here, the width of each electrode of the comb tooth isset to 3 μm, and the gap between the comb teeth is set to 3 μm. FIG. 6Bshows a case in which its aperture ratio is set to the maximum and theratio between the upper and lower parts is made 1:1.

FIG. 1A shows an example in which the ratio between the upper and lowerparts is changed while the aperture ratio is set to the maximum. Theratio between the upper and lower parts is changed without changing thebasic configuration in FIG. 6B. The ITO electrodes in the comb-teethshape are set, from the ITO electrode pattern, in the top rightdirection in the upper region 131 and set in the bottom left directionin the lower region 132. Here, the ratio of the upper region 131 is setto 30% of the whole.

FIG. 1B shows an example in which an ITO electrode pattern is verticallyprovided at the middle in the horizontal direction of the pixel and theproportions between the upper and lower parts are changed. The pixelregion 103 is divided into four regions 141 to 144. The ITO electrodesin the comb-teeth shape are set, from this ITO electrode pattern, inupper directions in the upper side regions 141 and 142 and in lowerdirections in the lower side regions 143 and 144. The manner ofextending the ITO electrodes in the comb-teeth shape is set such thatarms are stretched upward on the upper side of the pixel. On the otherhand, the form is set such that both arms are put down while spreadingto the right and left on the lower side of the pixel. Here, theproportion of the upper side regions 141 and 142 is set to 30% of thewhole.

FIG. 8A shows the essential configuration of the liquid crystal displaydevice. A TFT 801 has a gate connected to the gate line 114, a sourceconnected to the data line 113 and a drain connected to the transparentelectrode 111. A liquid crystal layer 802 has an end connected to thetransparent electrode 111 on the TFT substrate and the other endconnected to a common electrode (ground electrode) of an oppositesubstrate. A subsidiary capacitor 803 has an end connected to thetransparent electrode 111 through a contact region 701 and the other endconnected to the ground potential.

FIG. 8B is a cross-sectional view of the subsidiary capacitor 803 andthe surroundings. The subsidiary capacitor 803 is formed by providing aninsulating layer between metal layers 811 and 812. The metal layer 811is formed on the same layer as that of the TFT 801 (FIG. 8A) while it isnot connected to the source electrode of the TFT 801. The metal layer812 is also referred to as a subsidiary capacitor (Cs) layer hereafter.The Cs layer 812 is connected to the ground potential. The metal layer811 is connected to the contact region 701 through a contact hole 813.

Referring to FIG. 7 and FIG. 9, a more accurate layout of the electrodein a gridiron shape is explained. FIG. 7 corresponds to FIG. 6A, andFIG. 9 corresponds to FIG. 1B.

In FIG. 7, the electrode 812 (FIG. 8B) for the subsidiary capacitor (Cs)is formed in the horizontal direction at a middle part of the pixel, andthe contact region 701 is formed for contacting the ITO electrode 111and the metal layer 811 (FIG. 8B). The configuration is made such thatthe end of the electrode 702 in a gridiron-line shape is kept away fromthe contact region 701 as in an enlarged view shown at a lower part inFIG. 7.

FIG. 10 is a cross-sectional view of the TFT. Above a gate electrode1001, a source electrode 1002 and a drain electrode 1003 are formedthrough an insulating film 1011. Further, an ITO electrode 1005 isformed thereabove through an insulating film 1012. The ITO electrode1005 and the drain electrode 1003 are connected with each other througha contact hole 1004.

The lower part in FIG. 9 shows an enlarged view of the drain electrodeof the TFT and a contact region 901 of the ITO electrode. It isimportant that the ends of electrodes 903 in a gridiron-line shape areopen, and thus it is designed to form, as much as possible, a part in aslit shape interposed between the ends and the drain electrode. Anelectrode 902 in a gridiron-line shape is connected to the contactregion 901.

FIG. 11 is a cross-sectional view of a typical liquid crystal displaydevice. A liquid crystal layer 1102 is provided between an oppositesubstrate 1101 and a TFT substrate 1103. In the opposite substrate 1101,a glass substrate 1111, a color filter 1112 and an ITO electrode 1113are laminated in order. In the TFT substrate 1103, a glass substrate1124, an insulating layer 1123, an insulating layer 1122 and an ITOelectrode 1121 are laminated in order. Above a gate electrode 1131, asource electrode 1133 and a drain electrode 1132 are formed through theinsulating layer 1123. The ITO electrode 1121 is connected to the drainelectrode 1132.

FIGS. 12A and 12B show a liquid crystal display device in which a colorfilter 1223 is formed in a TFT substrate 1203. FIG. 12A is a plane viewof the liquid crystal display device. FIG. 12B is a cross-sectional viewtaken along a line II-II in FIG. 12A. A liquid crystal layer 1202 isprovided between an opposite substrate 1201 and the TFT substrate 1203.In the opposite substrate 1201, a glass substrate 1211 and an ITOelectrode 1212 are laminated. In the TFT substrate 1203, a glasssubstrate 1226, an insulating layer 1225, an insulating layer 1224, acolor filter 1223, an acrylic resin layer 1222 and an ITO electrode 1221are laminated in order. Above a gate electrode 1231, a source electrode1233 and a drain electrode 1232 are formed through the insulating layer1225. The ITO electrode 1221 is connected to the drain electrode 1232.

When the color filter 1223 is provided on the TFT substrate 1203, theelectrode pattern can freely be laid out. With the configuration of FIG.11, its brightness decreases by influence of a horizontal electric fieldfrom the data line, and the liquid crystal molecules tilt in a directiondifferent from a direction at a desired angle, which presents a problemthat the visual angle characteristics are poor. In contrast to theabove, when the color filter 1223 is provided in the TFT substrate 1203as shown in FIG. 12B, the data line hides behind the color filter 1223.Here, as for the slit electrode, an oblique electric field which occursbetween the self-pixel and an adjacent pixel causes an alignment defect.Therefore, conversely, the configuration is arranged so that theadjacent pixel is also used to improve the alignment. As shown in FIG.13A, a gap 1321 between the electrode of the adjacent pixel and theself-pixel is made equal to a gap 1322 between the slits in theself-pixel, and its phase of drive is matched with those of horizontallyadjacent pixels for display operation. Specifically, frame inversion orline inversion drive is performed. In this event, for example, when anentire gray display is performed, the distribution of the electric fieldin the self-pixel is completely the same as that between the pixels.Thus, no alignment defect occurs at all. In this case, the alignmentbecomes uniform in the vertical direction on the entire surface torealize excellent visual angle characteristics and a uniform, brightdisplay.

FIG. 13A shows ITO electrodes 1311 to 1316 corresponding to regions ofsix pixels. A contact region 1301 for connecting to the drain electrodeof the TFT is provided at the top left of each of the ITO electrodes1311 to 1316. The gap 1321 is a gap between each of the ITO electrodes1311 to 1316. The gap 1322 is a gap between the electrodes in agridiron-line shape in each of the ITO electrodes 1311 to 1316. The gaps1321 and 1322 are equal.

In FIG. 13C, a contact hole 1331 for establishing a connection with theTFT is provided at a part joining the gridiron lines at the middle ofthe pixel to stable the aperture ratio and alignment.

FIG. 13B is a cross-sectional view taken along a line I-I in FIGS. 13Aand 13C. In a TFT substrate 1342, a data line 1341 is provided under thegap between each of the ITO electrodes 1314 to 1316.

According to this embodiment, as shown in FIG. 12B, the pair ofsubstrates 1201 and 1203 are provided. The liquid crystal layer 1202 issandwiched between the pair of substrates 1201 and 1203, so that theliquid crystal molecules are vertically aligned with respect to thesubstrates 1201 and 1203 when no voltage is applied between thesubstrates 1201 and 1203, and the liquid crystal molecules tilt in aplurality of directions to be almost parallel to the substrates 1201 and1203 by applying a voltage between the substrates 1201 and 1203 (seeFIGS. 1A and 18). In the liquid crystal layer 1202, when a voltage isapplied, the proportion of the region 131 where the liquid crystalmolecules tilt in a direction of 0 degrees to 180 degrees differs fromthe proportion of the region 132 where the liquid crystal molecules tiltin a direction of 180 degrees to 360 degrees with the angle beingdefined counterclockwise with the right direction on the screen being 0degrees as shown in FIG. 1A.

Alternatively, in the liquid crystal layer 1202, when a voltage isapplied, the proportion of the regions 141 and 142 where the liquidcrystal molecules tilt in directions of 45 degrees and 135 degrees isdifferent from the proportion of the regions 143 and 144 where theliquid crystal molecules tilt in directions of 225 degrees and 315degrees with the angle being defined counterclockwise with the rightdirection on the display screen being 0 degrees as shown in FIG. 1B. Inthe liquid crystal layer 1202, the proportion of the regions 141 and 142where the liquid crystal molecules tilt in the directions of 45 degreesand 135 degrees is preferably 40% or less of the whole.

As shown in FIG. 1B, the pixel electrode, which is a pixel electrode ina gridiron shape with lines having a width of 10 μm or less and a gap of10 μm or less, is provided in the TFT substrate 1203 (FIG. 12B). In theliquid crystal layer 1202, alignment directions of the liquid crystalmolecules are controlled by the pixel electrode so that the liquidcrystal molecules tilt in four directions. The pixel electrode has ashape in which the gridiron lines extend in directions of 45 degrees,135 degrees, 225 degrees and 315 degrees, so that the liquid crystalmolecules tilt in four directions of 45 degrees, 135 degrees, 225degrees and 315 degrees respectively in the liquid crystal layer 1202.

The thin film transistor includes the gate, the source and the drain. Asshown in FIG. 9, the pixel electrode has the contact region 901 forconnecting to the drain of the thin film transistor, and the slit isprovided between at least the parts 903 of a plurality of gridiron linesand the contact region 901. The gate line is connected to the gate ofthe thin film transistor. In the pixel electrode, the gridiron line 902of the plurality of gridiron lines, located at the nearest position ofthe gate line, is connected to the contact region 901.

As shown in FIG. 13A, as for the pixel electrode, the gap 1322 in theself-pixel electrode in a gridiron shape is equal to the gap 1321between the self-pixel electrode and the adjacent pixel electrode. Asshown in FIG. 12A, the thin film transistor is connected to the pixelelectrode 1221 in the TFT substrate 1203. The color filter layer 1223 isformed in the TFT substrate 1203.

As described above, a display with excellent visual characteristics canbe realized according to this embodiment.

Second Embodiment

Referring to FIG. 14 and FIG. 15, problems of the MVA-mode liquidcrystal display device are explained. FIG. 14 shows the MVA-mode liquidcrystal display device. Sits 1405 are provided in an ITO pixel electrode1404 on the TFT substrate side, and protrusions 1401 are formed, using aresist, on an ITO electrode of the opposite substrate. Further, a gateline 1402, a data line 1403 and a subsidiary capacitor forming electrode1406 are formed on the TFT substrate. The pixel electrode is dividedinto four regions 1411 to 1414. The liquid crystal molecules in theregions 1411 to 1414 are aligned in directions of the liquid crystalmolecules A1, B2, A2 and B1 in FIG. 4A respectively. In comparison tothe configuration of a TN-type display here, it is necessary to form aresist pattern on the ITO electrode of the opposite substrate, whichincreases the number of processing steps, resulting in increased cost.

FIG. 15 shows a case in which the ITO electrode on the oppositesubstrate is provided with a slit 1504. The TFT substrate is formed witha gate line 1501, a data line 1502, a subsidiary capacitor formingelectrode 1505 and an ITO electrode 1503. Black arrows 1521 showdirections of alignment control by the slit electrode 1504. White arrows1522 show directions of alignment control by the gate line 1501 and thedata line 1502. In regions 1511, response is delayed because of two ormore directions of alignment control.

Further, in comparison to the TN-type display, it is necessary toprovide the slit 1504 in the ITO electrode of the opposite substrate,which increases the number of processing steps, resulting in increasedcost in this case. When the color filter is provided on the oppositesubstrate, the color filter layer is exposed within a part of the slit1504, which presents a problem that reliability decreases due todropping-out of impurities from the color filter layer. Further, sincethe direction of alignment control by the data line 1502 or the gateline 1501 differs by 45 degrees from that by the slit electrode 1504, ittakes time for the alignment to stabilize, which presents a problem thatresponse is slow.

FIG. 16 shows a pattern of the pixel electrode according to thisembodiment of the invention. The TFT substrate is formed with a gateline 1601, a data line 1602 and fine slit pixel electrodes 1621 and1622.

Black arrows 1612 show directions of alignment control by the fine slitelectrodes 1621 and 1622. White arrows 1611 show directions of alignmentcontrol by the gate line 1601 and the data line 1602.

Near the data line 1602 the fine slit pixel electrodes 1622 are providedin the horizontal direction (perpendicular to the data line). Near thegate line 1601 the fine slit pixel electrodes 1621 are provided in thevertical direction (perpendicular to the gate line). Further, as a partjoining the electrodes, an ITO electrode 1613 is vertically extended atthe middle of the pixel, and ITO electrodes 1623 are extended towardintersections between the data lines 1602 and the gate lines 1601. Theangle of the ITO electrodes 1623 intersecting each other is 45 degrees.The ITO electrode 1613 is formed in a backbone shape, on which thealignment direction of the liquid crystal molecules is determined byinfluence of alignment of liquid crystal molecules near the gate lines1601. Here, the electrode width of the fine electrodes 1621 and 1622 isset to about 3 μm, and the width of the slit between the electrodes 1621and 1622 is also set to about 3 μm.

On the fine electrodes 1621 and 1622, the directions, in which theliquid crystal molecules tilt when a voltage applied between theelectrode on the TFT substrate and the electrode on the oppositeelectrode, are parallel to the directions in which the fine electrodesextend. This operation is explained using FIGS. 17A and 17B.

FIG. 17A shows a case of a rough pixel electrode pattern. A liquidcrystal layer 1702 is provided between an opposite substrate 1701 and aTFT substrate 1703. On the opposite substrate 1701, an ITO transparentelectrode is formed on the entire surface. The electrode patterninterval on the TFT substrate 1703 is large. In a region 1711, theliquid crystal molecules tilt in accordance with the gradient of theelectric field since gaps of the electrodes are large. The liquidcrystal molecules tilt in the horizontal direction in FIG. 17A becausethe region is distant from a region where the liquid crystal moleculestilt in an opposite direction to produce no mutual interference.

FIG. 17B shows a case of a fine electrode pattern on the TFT substrate1703. In a region 1721, the liquid crystal molecules tilting inaccordance with the gradient of the electric field collide with eachother and can not tilt since gaps between the electrodes are small. Inorder to escape from the stress, liquid crystal molecules 1722 tilt in adirection parallel to the electrode (direction perpendicular to thepaper surface of FIG. 17B).

This embodiment employs the above principle, in which, at parts wherethe fine electrodes 1622 extending perpendicular to the data lines 1602exist as shown in FIG. 16, the liquid crystal molecules tilt in thehorizontal direction by the influence of the fine electrodes 1622 andthe horizontal electric fields from the data lines 1602. Since thedirection of alignment control by the fine electrodes 1622 matches thedirection of alignment control by the horizontal electric fields fromthe data lines 1602, the liquid crystal molecules simply tilt here. Onthe other hand, at parts where the fine electrodes 1621 extendingperpendicular to the gate lines 1601 exist, the liquid crystal moleculestilt in the vertical direction by the influence of the fine electrodes1621 and the horizontal electric fields from the gate lines 1601. Sincethe direction of alignment control by the fine electrodes 1621 matchesthe direction of alignment control by the horizontal electric fieldsfrom the gate lines 1601, the liquid crystal molecules simply tilt here.

Since the alignment control is simply exerted on the liquid crystalmolecules as described above, it is unnecessary to provide on theopposite substrate a special structure such as a protrusion or a slit.

FIG. 16 is explained in more detail. The ITO transparent electrode isprovided within the pixel region surrounded by the gate lines 1601 andthe data lines 1602, and a display voltage is applied thereto by theTFT. The ITO electrode is patterned into a comb-teeth shape such thatthe direction of the comb is set perpendicular to the data lines 1602near the data lines 1602 and perpendicular to the gate lines 1601 nearthe gate lines 1601. The teeth of the comb join the electrode 1613 whichvertically extends at the middle of the pixel. This electrode 1613 likea backbone is in the shape of a letter Y which extends toward theintersections between the data lines 1602 and the gate lines 1601. Whenthe angle between opening arms of the letter Y is set to a range from 30degrees to 120 degrees, excellent alignment can be obtained. Here, thewidth of the ITO electrode of the slit electrode is set to 3 μm to 5 μm,and the ITO gap between the slits is set to 2 μm to 5 μm.

FIG. 18 shows a case in which the angle between the opening arms isabout 60 degrees. Electrodes 1821 in the comb-teeth shape extending inthe vertical direction (perpendicular to gate lines 1801) have greaterlengths. In this case, it is possible to effectively utilize thehorizontal electric fields from the gate lines 1801.

FIGS. 19A to 19C show enlarged views of patterns of the ITO electrode.

FIG. 19A shows the simplest configuration, in which the width of the ITOelectrode in the comb-tooth shape is fixed. The liquid crystal moleculestilt in the horizontal direction in FIG. 19A in a region 1902, theliquid crystal molecules tilt in the vertical direction in FIG. 19A in aregion 1903, and the liquid crystal molecules tilt in an obliquedirection of 45 degrees in FIG. 19A in a region 1901.

In FIG. 19B, the direction of the electrodes in the comb-teeth shape istilted θ degrees. The directions, in which the electrodes in thecomb-teeth shape extending upward from open arms of a backbone extend,are tilted from the upward direction to the directions of the open arms.In other words, electrodes 1922 in the comb-teeth shape, which areelectrodes near the gate line, are tilted θ degrees from thelongitudinal direction of an electrode 1921 in a backbone shape.Electrodes in the comb-teeth shape 1923, which are electrode near thedata line, are tilted θ degrees from the vertical direction of theelectrode 1921 in the backbone shape. The tilted angle θ was changedfrom 1 degree to 45 degrees.

In a region 1911, the liquid crystal molecules tilt in an obliquedirection of 45 degrees in FIG. 198. The tilts of the liquid crystalmolecules in the regions 1902 and 1903 in FIG. 19A differ from eachother by 90 degrees. Since the difference between regions 1912 and 1913in FIG. 19B in tilt of the liquid crystal molecules therein is smallerthan 90 degrees, the tilts of the liquid crystal molecules graduallychange between the regions 1911 and 1913.

FIG. 19C shows a configuration when the shape of the electrode istapered. The angle θ of the tapered electrodes 1931 and 1932 is set hereto about 1 degree to about 20 degrees. The effects of tapering the shapeof the electrode are explained. FIG. 20A shows a case in which fineelectrodes 2001 and 2002 are parallel to each other. A liquid crystalmolecule 2003 near the fine electrode 2001 differs from a liquid crystalmolecule 2004 near the fine electrode 2002 in tilt by 180 degrees. FIG.20B shows a case in which the shape of fine electrodes 2011 and 2012 istapered. The difference in tilt between a liquid crystal molecule 2013near the fine electrode 2011 and a liquid crystal molecule 2014 near thefine electrode 2012 is smaller than 180 degrees. The tilts of the liquidcrystal molecules 2013 to 2015 gradually change.

FIGS. 21A and 21B show a configuration of a case of utilizing asubsidiary capacitor forming Cs line. FIG. 21A is a plane view of theliquid crystal display device. A horizontal electric field is formedfrom a Cs line 2104 similarly to a gate line 2102 or a data line 2103.This horizontal electric field is positively utilized.

A metal layer 2105, which corresponds to the metal layer 811 in FIG. 8B,is connected to an ITO pixel electrode 2101. It is important to pointthe tips of the comb of the electrode in the comb-teeth shape here, asin the case shown in FIG. 16. FIG. 18, and FIGS. 19A to 19C, to theelectrode which causes the horizontal electric field (the data line orthe gate line in FIG. 16, FIG. 18, and FIGS. 19A to 19C).

In FIG. 21A, as the electrode in the comb-teeth shape, electrodes in acomb-teeth shape are extended upward and downward and leftward andrightward in each of an upper half part 2101 a and a lower half part2101 b of a pixel.

FIG. 21B is a cross-sectional view taken along a line 2106 in FIG. 21A.An ITO pixel electrode 2121 is formed on the entire surface of anopposite substrate 2111. In a TFT substrate 2112, a metal layer 2133 isformed above a Cs line 2134 through an insulating film 2132. The metallayer 2133 and an ITO pixel electrode 2131 are connected with eachother. The Cs line 2134 corresponds to the Cs line 2104 in FIG. 21A, andthe metal layer 2133 corresponds to the metal layer 2105 in FIG. 21A. Asdescribed above, an oblique electric field 1341 produced from the Csline 2134 can be positively utilized for alignment.

It should be noted that, a backbone region may be provided in the ITOpixel electrode 2101 in each of the regions 2101 a and 2101 b as shownin FIG. 22.

FIG. 23A shows an example in which a pixel electrode 2301 is extended tothe top right, the top left, the bottom left and the bottom right. TheTFT substrate is formed with a gate line 2302, a data line 2303 and a Csline 2304 in addition to the pixel electrode 2301. The pixel electrode2301 includes an electrode 2305 parallel to the Cs line 2304.

FIG. 23B shows a configuration in which the Cs line 2304 is positivelyutilized. In a pixel electrode 2311, regions 2311 a and 2311 b havingdifferent alignments are formed in a cross shape in an upper half partand a lower half part of each pixel. The regions 2311 a and 2311 b areconnected, with each other via a pixel electrode 2312.

In FIG. 21A, a transparent electrode for transmitting a voltage from theTFT is provided across the Cs line 2104. The ITO transparent electrode2101 is set here in such a manner to extend along the Cs line 2104 onthe Cs line 2104. This realizes a subsidiary capacitor.

FIG. 24 shows a configuration in which the aforementioned liquid crystalpanel is sandwiched between a pair of λ (wavelength)/4 plates. A liquidcrystal panel 2403 is sandwiched between quarter wave plates 2402 and2404, and further both sides thereof are sandwiched between polarizingplates 2401 and 2405. An absorption axis 2411 of the polarizing plate2401 deviates by 45 degrees from the horizontal direction in FIG. 24. Anoptical axis 2412 of the quarter wave plate 2402 deviates by 90 degreesfrom the horizontal direction in FIG. 24. An optical axis 2414 of thequarter wave plate 2404 is in the same direction as the horizontaldirection in FIG. 24. An absorption axis 2415 of the polarizing plate2405 deviates by 135 degrees from the horizontal direction in FIG. 24.The polarizing plates 2401 and 2405 absorb light components in theabsorption axes 2411 and 2415 respectively. The quarter wave plates 2402and 2404 convert between linearly polarized light and circularlypolarized light and then output it. The liquid crystal panel 2403 issandwiched between the pair of quarter wave plates 2402 and 2404,resulting in improved brightness.

FIG. 25A is the same configuration as in FIG. 23B, the distribution ofthe amount of transmitted light in the upper half pixel region 2311 a isshown in FIGS. 25B and 25C. FIG. 25B shows a distribution without aquarter wave plate, in which a black region in a cross shape appears inthe pixel. This is because the liquid crystal molecules tilt in adirection perpendicular or parallel to the optical axis of thepolarizing plate. FIG. 25C shows a distribution in a case of employingthe quarter wave plates 2402 and 2404 as shown in FIG. 24, in which ablack region exists only at the central part of the pixel, realizing abight display.

According to this embodiment, as shown in FIG. 16, the pixel electrodeis a pixel electrode in the comb-teeth shape or in the slit shape, inwhich the directions of the comb teeth extend toward the gate lines 1601near the gate lines and toward the data lines 1602 near the data lines.

As shown in FIG. 21A, the Cs line (subsidiary capacitor formingelectrode line) 2104 extends in the horizontal direction at the middleof the pixel. The pixel electrode is formed divided into the upper andlower parts with the subsidiary capacitor forming electrode line 2104 asa boundary and extends, near the subsidiary capacitor forming electrodeline 2104, in the same direction as that of the subsidiary capacitorforming electrode line to overlap therewith.

Further, as shown in FIG. 16, in the pixel electrode, the electrode 1613is formed in the backbone shape in the vertical direction at the middleof the pixel, and the electrode parts 1623, which join the electrodes1621 in the comb-teeth shape toward the gate lines 1601 and theelectrodes 1622 in the comb-teeth shape toward the data lines 1602,extend in the four directions from the electrode 1613 in the backboneshape to be in the shape of arms of the letter Y.

As shown in FIG. 21A, in the pixel electrode, the directions of the combteeth extend, near the subsidiary capacitor forming electrode line 2104,toward the subsidiary capacitor forming electrode line. The pixelelectrode has electrodes in the shape of arms of the letter Y, whichjoin the electrodes in the comb-teeth shape toward the subsidiarycapacitor forming electrode line 2104 and the electrodes in thecomb-teeth shape toward the data lines 2103, and electrodes in the shapeof arms of the letter Y, which join the electrodes in the comb-teethshape toward the gate lines 2102 and the electrodes in the comb-teethshape toward the data lines 2103.

The angle formed by the aforesaid electrodes in the shape of arms of theletter Y is preferably 30 degrees or more to 150 degrees or less.Further, as shown in FIG. 19B, in the pixel electrode, the directions ofthe electrodes 1922 in the comb-teeth extending toward the gate lines,near the data lines, extend tilting toward the data lines, and thedirections of the electrodes 1923 in the comb-teeth extending toward thedata lines, near the gate lines, extend tilting toward the gate lines.Further, as shown in FIG. 19C, the shape of the comb teeth of the pixelelectrode is made such that the tip parts of the teeth are narrower ortapered.

As shown in FIG. 21A, in the pixel electrode, the electrode, which isprovided across the subsidiary capacitor forming electrode line 2104 totransmit a voltage from the drain of the thin film transistor, extends,near the subsidiary capacitor forming electrode line 2104, in the samedirection as that of the subsidiary capacitor forming electrode line tooverlap therewith.

Further, as shown in FIG. 24, the pair of quarter wave plates 2402 and2404, of which optical axes are perpendicular to each other, interposethe liquid crystal panel (the pair of substrates interposing the liquidcrystal layer therebetween) 2403 therebetween.

As described above, the use of this embodiment enables realization of aliquid crystal display which is bright and has a wide viewing angle.

Third Embodiment

In order to further improve the visual angle characteristics of theMVA-mode liquid crystal display device, a film configuration as shown inFIG. 26 is proposed. A liquid crystal layer 2605 is sandwiched between apair of retardation films 2604 and 2606 having in-plane retardation.Further, both sides thereof are sandwiched between a pair of negativeretardation films 2603 and 2607. Furthermore, both sides thereof aresandwiched between a pair of polarizers 2602 and 2608. Further, bothsides thereof are sandwiched between a pair of protective layers 2601and 2609. An absorption axis 2612 of the polarizer 2602 and anabsorption axis 2618 of the polarizer 2608 deviate from each other by 90degrees. An optical axis 2614 of the retardation film 2604 and anoptical axis 2616 of the retardation film 2606 deviate from each otherby 90 degrees. The absorption axis 2612 of the polarizer 2602 and theoptical axis 2614 of the retardation film 2604 deviate from each otherby 90 degrees. As for the visual angle characteristics, a range of acontrast 10 or more is achieved at an inclined angle of ±80 degrees ormore in all directions. However, the brightness can not be improved.

On the other hand, a technique using a circularly polarizing plate asshown in FIG. 27 is proposed as a technique for improving thebrightness. A liquid crystal panel 2706, in which a liquid crystal layeris sandwiched between two substrates, is sandwiched between a pair oftriacetylcellulose (TAC) films 2705 and 2707. Further, both sidesthereof are sandwiched between a pair of quarter wave films 2704 and2708. Furthermore, both sides thereof are sandwiched between a pair ofTAC films 2703 and 2709. Further, both sides thereof are sandwichedbetween a pair of polyvinyl alcohol (PVA) polarizing layers 2702 and2710. Further, both sides thereof are sandwiched between a pair of TACfilms 2701 and 2711.

An absorption axis 2722 of the polarizing layer 2702 deviates by 90degrees from the horizontal direction in FIG. 27. An optical axis 2724of the quarter wave film 2704 deviates by 45 degrees from the horizontaldirection in FIG. 27. An optical axis 2728 of the quarter wave film 2708deviates by 135 degrees from the horizontal direction in FIG. 27. Anabsorption axis 2730 of the polarizing layer 2710 is in the samedirection as the horizontal direction in FIG. 27.

While the brightness is improved by 20% to 50% with this configuration,it is impossible to attain the visual angle characteristics which can beachieved by the configuration shown in FIG. 26. Although a range of acontrast 10 or more is achieved at ±80 degrees in top and bottom andright and left directions, it is achieved only at ±50 degrees in 45degree oblique directions.

This embodiment of the invention has a configuration having bothcharacteristics of FIG. 26 and FIG. 27.

FIG. 28A shows the simplest principle configuration in this embodiment.A λ (wavelength)/2 plate 2802 is sandwiched between a pair of polarizinglayers 2801 and 2803. An absorption axis 2811 of the polarizing layer2801 is in the same direction as the horizontal direction in FIG. 28A.An optical axis 2812 of the half wave plate 2802 is also in the samedirection as the horizontal direction in FIG. 28A. An absorption axis2813 of the polarizing layer 2803 deviates by 90 degrees from thehorizontal direction in FIG. 28A.

The polarizing layers 2801 and 2803 denote PVA polarizing layers, and astate is shown here in which there are no TAC films though a polarizingplate is typically provided with a pair of triacetylcellulose (TAC)films on both sides of the PVA polarizing layers. The half wave plate2802 is provided between the pair of polarizing layers 2801 and 2803,where the retardation ((nx+ny)/2−nz)×d in a direction perpendicular tothe film of the half wave plate 2802 is zero. In the above equation, nx,ny and nz are refractive indexes in respective directions, and d is athickness. The optical axis 2812 of the half wave (retardation) plate2802 is parallel or perpendicular to the absorption axes 2811 and 2813of the adjacent polarizing layers 2801 and 2803. FIG. 28B shows thestate of leaking light in this case, in which it is found that there isalmost no leaking light in all directions.

The configuration of the entire liquid crystal panel is made to besubstantially the same as this configuration. In other words, opticalfilms and a liquid crystal layer are laminated on this configuration,but they cancel each other out so that substantially nothing existsthereon to make the configuration substantially the same as in FIG. 28A.

FIG. 29A shows a case in which a pair of quarter wave films 2901 and2902 are laminated in such a manner that their optical axes 2911 and2912 are perpendicular to each other. The quarter wave films 2901 and2902 are inserted between the half wave plate 2802 and the polarizinglayer 2803. The directions of the optical axes 2911 and 2912 of thequarter wave plates (films) 2901 and 2902 are set here to form angles of45 degrees with the absorption axes 2811 and 2813 of the polarizinglayers 2801 and 2803 respectively. The negative retardation of thequarter wave plates 2901 and 2902 is also set to zero. The quarter waveplates 2901 and 2902 convert between linearly polarized light andcircularly polarized light. FIG. 29B shows the state of leaking light inthis case, in which it is found that there is very little leaking lightin all directions.

In FIG. 30A, a liquid crystal layer 3001 capable of vertical alignmentand a film 3002 having a negative retardation

((nx+ny)/2−nz)×d<0

only in a direction perpendicular to the film surface are furtherlaminated. The vertically aligned liquid crystal layer 3001 has apositive retardation, anisotropy in refractive index of a liquidcrystal,

Δn×cell thickness d>0

only in a direction perpendicular to the liquid crystal layer 3001. Thenegative retardation of the aforesaid film 3002 and the positiveretardation of the liquid crystal layer 3001 are set to be equal to eachother to optically cancel out each other completely. The Δn is n//−n⊥,n// is a refractive index in the longitudinal direction of a liquidcrystal molecule, and n⊥ is a refractive index in a directionperpendicular to the longitudinal direction of the liquid crystalmolecule.

The laminated liquid crystal layer 3001 and the film 3002 are insertedbetween the pair of quarter wave films 2901 and 2902. The Δn×d of thefilm 3002 is the same as that of the liquid crystal layer 3001. The Δnof the film 3002 is nx−nz.

When the configuration in FIG. 28A is employed, leakage of light frompolarizing layers 2801 and 2803 in a cross-Nicol arrangement is actuallyvery little when viewed from any direction, and this operation isexplained. The polarizing layers 2801 and 2803 in a cross-Nicolarrangement when observed from an inclined angle is considered here. Theabsorption axes 2811 and 2813 of the polarizing layers 2801 and 2803 areperpendicular to each other when they are viewed from the front. Whenviewed from an inclined angle, the absorption axes 2811 and 2813 of thepolarizing layers 2801 and 2803 are still perpendicular to each other,from an a direction in FIG. 28A, without leakage of light. In contrastto the above, when they are viewed from a b direction in FIG. 28A, theabsorption axes 2811 and 2813 of the polarizing layers 2801 and 2803 arenot perpendicular to each other. This can easily be understood byplacing, for example, two pencils to be perpendicular to each other andthen observing them from a direction such as the b direction. Changingthe polarized state of incident light to prevent the light from leakingtherefrom even in the b direction is the operation of the half waveplate 2802 in FIG. 28A. In consideration of the case of observing fromthe a direction, the angles of the absorption axes 2811 and 2813 of thepolarizing layers 2801 and 2803 are set in the top left direction on theincident side and the top right direction on the exit side, and theoptical axis 2812 of the half wave plate 2802 is set in the top rightdirection. With an inclined angle in the b direction here, theabsorption axis on the incident side deviates from the top left towardthe left direction, and the absorption axis on the exit side deviatesfrom the top right toward the right direction. On the other hand, theoptical axis of the half wave plate 2802 having a negative retardationof 0 does not move from the top left direction. Therefore, thepolarization direction of the incident light and the half wave(retardation) plate 2802 form a certain angle therebetween in the bdirection. Then, the incident light, of which the polarization directionis rotated because of its half wave retardation, is brought intolinearly polarized light to exit from the retardation plate 2802. Theexit light, of which the polarization direction matches the direction ofthe absorption axis of the polarizing layer on the exit side, iscompletely absorbed. Therefore, there is almost no leaking light whenthe polarizing layers are observed from any direction as shown in FIG.28B.

Next, the operations of the quarter wave plates 2901 and 2902, of whichoptical axes are perpendicular to each other, employed in FIG. 29A willbe described. As described above in the description of the half wave(retardation) plate 2802, the directions of the optical axes thereof areunchangeable even when observed at an inclined angle because theretardation in the direction perpendicular to the film surface is 0.Accordingly, the optical axes 2911 and 2912 of the quarter wave plates2901 and 2902, which are perpendicular to each other at the front, areperpendicular to each other when observed in any direction and at anyinclined angle. As a result, the effects of the quarter wave plates 2901and 2902 are cancelled out each other, which comes to the same thing asif there exists nothing.

Next, the operation of the film 3002 having negative retardation in FIG.30A which is laminated with the liquid crystal layer 3001 is described.The negative retardation of the film 3002 here is equal to the positiveretardation of the vertically aligned liquid crystal layer 3001. Theoptical effects of the two layers in such a relationship as describedabove are completely cancelled out, which comes to the same thing as ifthere exists nothing. Therefore, the black display as the liquid crystaldisplay is black when viewed from any direction. FIG. 30A shows a liquidcrystal panel of which the inside of the pixel is broadly divided intofour types where the liquid crystal molecules tilt in the top right, thetop left, the bottom left and the bottom right direction with theapplication of voltage. It can be understood that, as shown in FIG. 30B,the contrast of 10 or more is realized in all directions.

The optical axes 2911 and 2912 of the quarter wave plates 2901 and 2902are perpendicular to each other and set to form angles of 45 degreeswith the absorption axes 2811 and 2813 of the polarizing layers 2801 and2803, which configuration corresponds to a so-called a circularlypolarizing plate. The quarter wave plates 2901 and 2902 serve a functionof bringing linearly polarized light passed through the polarizing layerinto circularly polarized light. The optical effects of each film andthe vertically aligned liquid crystal layer are cancelled out each otherto create no optical effect in the description by now, but the state iscompletely changed when a voltage is applied across the liquid crystallayer 3001. Specifically, the liquid crystal layer 3001 has an opticaleffect to realize a white display. Further, the quarter wave retardationplates 2901 and 2902 improve the brightness of the white display at afront visual angle as mentioned in the above description.

The half wave retardation plate 2802 and the quarter wave retardationplates 2901 and 2902 are realized by stretching a polycarbonate film ora norbornene-based film. As for the stretching manner, the film isstretched in a plane and is additionally drawn in the directionperpendicular thereto with a stress exerted thereon.

The half wave retardation plate 2802 here is also realized by laminatingtwo quarter wave retardation plates. Such a film is commerciallyavailable, by names such as NZ film from Nitto Denko Co., Ltd. or SZfilm from Sumitomo Chemical Co., Ltd.

The film 3002 having the negative retardation is realized by stretchinga polycarbonate film or a norbornene-based film in two directions or byapplying a resin onto a film having no optical effect. Such a film isalso commercially available from Nitto Denko Co., Ltd., and a film bythe name of VAC film is available from Sumitomo Chemical Co., Ltd.

As the liquid crystal panel 3001, the MVA-mode liquid crystal panelwhich is commercially available from Fujitsu Co., Ltd. is used. As forthe alignment direction thereof, one pixel is broadly divided into fourtypes of regions where the liquid crystal molecules tilt in directionsof the top right, the top left, the bottom left and the bottom rightdirection respectively by applying a voltage.

As the polarizing plates 2801 and 2803, a triacetylcellulose (TAC) filmis typically used as a holding material of the polarizing plate, but ifthe TAC films exist between the polarizing layers 2801 and 2803, and,the liquid crystal layer 3001 respectively, their optical effectsproduce adverse effect. Therefore, this holding material is used only onone side in laminating films and should not be set on the liquid crystallayer side. Such a polarizing plate, in which the TAC film is actuallyprovided only on one side of a polarizing layer, is commerciallyavailable from, for example, Sumitomo Chemical Co., Ltd. by name ofUltra-Thin-Polarizer. Optical films are laminated on this polarizingplate to realize the film configuration shown in FIG. 30A.

FIG. 30B is a calculation example of the visual angle characteristicswhen the aforementioned films and the liquid crystal layer are laminatedas shown in FIG. 30A.

In the configuration in FIG. 30A, the visual angle characteristics areas shown in FIG. 30B, in which the direction with particularly highcontrast is, as is clear from FIG. 30B, the top right, the top left, thebottom left and the bottom right direction. Particularly, a wide visualangle is needed in the visual directions of the top and the bottom andthe right and the left, and the configuration in FIG. 31A is adopted tomeet the need. The directions of the absorption axes of the polarizinglayers and the directions of the optical axes of the films are rotatedhere from those in FIG. 30A by 45 degrees. The calculation result of thevisual angle characteristics in this event is shown in FIG. 31B. Thecontrast is 10 or more in all directions and further, the visual anglecharacteristics are vertically and horizontally symmetric withparticularly wide visual angle ranges at the top and the bottom and theright and the left. This enables a bright display with perfect viewingangle characteristics.

The measured value of the visual angle characteristics of a prototype ofa liquid crystal panel is shown in FIG. 32. Since the characteristics ofthe films are not perfect, they differ from the calculationcharacteristics, but a wide viewing angle could be obtained. Inaddition, the display brightness of white at the front could beimproved, at the same time, by 20% as compared with the case of adoptingno films.

Although the description has been made by now assuming that the halfwave plate 2802 in FIG. 28A is employed, more preferable visual anglecharacteristics can be obtained if a liquid crystal panel laminated witha pair of special half wave plates is used. This arrangement is reportedby Tohoku University in SID00.

Two films having a retardation of half wavelength are laminated, inwhich a film having a Nz constant of 0.25 and a film having a Nzconstant of 0.75,

Nz constant=(nx−nz)/(nx−ny)

where nz is a refractive index in a direction perpendicular to the filmsurface, nx is a refractive index in a direction parallel to the opticalaxis of the film, and ny is a refractive index in a film in-planedirection perpendicular to the optical axis of the film, are laminatedin such a manner that optical axes thereof are parallel to each other,and retardation axes of the films are set to be parallel orperpendicular to absorption axes of adjacent polarizing layers. Thisarrangement is employed in place of that in FIG. 28A and further, filmsand a liquid crystal layer are arranged as shown in FIG. 29A, FIG. 30Aand FIG. 31A.

Moreover, when the values of (nx−nz)/(nx−ny) of the two films are 0.5 orless and 0.5 or more respectively, and the sum thereof is about 1 suchas, preferably, 0.25 and 0.75, or 0.15 and 0.85, the same excellentlight leakage characteristics can be obtained.

As for the negative retardation of the above-described film, it isdifficult in fabrication to bring the negative retardation completely to0 in the half wave plates and the quarter wave plates. It was found thatexcellent viewing angle characteristics can be obtained when the rangeof each negative retardation thereof is ±20 nm or less, preferably ±10nm or less.

According to this embodiment, as shown in FIG. 31A, the half wave plate2802, in which a film having a retardation of half wavelength islaminated, has a retardation ((nx+ny)/2−nz)×d in a directionperpendicular to the film surface (where nz is a refractive index in adirection perpendicular to the film surface, nx is a refractive index ina direction parallel to the optical axis of the film, ny is a refractiveindex in a film in-plane direction perpendicular to the optical axis ofthe film, and d is a thickness of the film) of 0 or ±20 nm or less, andthe optical axes of the films are parallel or perpendicular to theabsorption axis of the adjacent polarizing layer 2801.

Alternatively, the half wave plate 2802, in which two films having aretardation of half wavelength are laminated, may have values(nx−nz)/(nx−ny) of the two films of 0.5 or less and 0.5 or morerespectively, where nz is a refractive index in a directionperpendicular to the film surface, nx is a refractive index in adirection parallel to the optical axis of the film, and ny is arefractive index in a film in-plane direction perpendicular to theoptical axis of the film, and the optical axes of the two films may beparallel to each other, and may be parallel or perpendicular to theabsorption axis of the adjacent polarizing layer 2801.

The film 3002 has a negative retardation equal to the value of Δn×d ofthe liquid crystal layer 3001 (where Δn is n//−n⊥, n// is a refractiveindex in the longitudinal direction of a liquid crystal molecule, n⊥ isa refractive index in a direction perpendicular to the longitudinaldirection of the liquid crystal molecule, and d is a thickness), and isprovided adjacent to the liquid crystal layer 3001.

The pair of quarter wave plates 2901 and 2902 have a negativeretardation of 0 or ±10 nm or less, and provided to interpose the liquidcrystal layer 3001 and the film 3002 therebetween. The optical axes ofthe pair of quarter wave plates 2901 and 2902 are perpendicular to eachother and form angles of 45 degrees with the absorption axes of the pairof polarizing layers 2801 and 2803. The direction of the absorption axisof the polarizing layer on the light incident side is set at any of 0degrees, 45 degrees, 90 degrees and 135 degrees with the right directionon the screen being 0 degrees.

As shown in FIG. 31A, the directions of the absorption axes of thepolarizing layers are adjusted so that the directions in which thecontrast becomes maximum are the top and bottom and right and leftdirections while the relationship between the optical axes of thepolarizing layer on the light incident side, the polarizing layer on thelight exit side, the quarter wave plates and the half wave plates inFIG. 30A is maintained.

In the liquid crystal layer 3001, the liquid crystal molecules arevertically aligned where no voltage is applied thereto, and the liquidcrystal molecules are aligned to tilt, broadly, in two or more differentdirections in a pixel where a voltage is applied thereto. Preferably, inthe liquid crystal layer 3001, the liquid crystal molecules tilt broadlyin four different directions of the top right, the top left, the bottomleft and the bottom right direction in a pixel where a voltage isapplied thereto, and the alignment of the liquid crystal is controlledusing the slits provided between the electrodes and/or the projections(protrusions) provided on the electrodes.

As described above, the use of this embodiment enables realization of aliquid crystal display which is bright and has a wide viewing angle.

Fourth Embodiment

In order to further improve the visual angle characteristics of theMVA-mode liquid crystal display device, a film configuration as shown inFIG. 33 is proposed. A liquid crystal layer 3304 is sandwiched between apair of retardation films 3303 and 3305 having in-plane retardation.Further, both sides thereof are sandwiched between a pair of negativeretardation films 3302 and 3306. Furthermore, both sides thereof aresandwiched between a pair of polarizing plates 3301 and 3307. Anabsorption axis 3311 of the polarizing plate 3301 and an absorption axis3317 of the polarizing plate 3307 deviate from each other by 90 degrees.An optical axis 3313 of the retardation film 3303 and an optical axis3315 of the retardation film 3305 deviate from each other by 90 degrees.The absorption axis 3311 of the polarizing plate 3301 and the opticalaxis 3313 of the retardation film 3303 deviate from each other by 90degrees.

As for the visual angle characteristics, a range of a contrast 10 ormore is achieved at an inclined angle of ±80 degrees or more in alldirections. However, two films are used, and special film have been usedwhich have a relationship

nx>ny>nz

which are refractive indexes of the films in some cases.

As shown in FIG. 34, this embodiment of the invention realizes a displayhaving excellent viewing angle characteristics without using suchspecial films. In this embodiment, only one film 3402 is added for useto polarizing plates 3401 and 3404, and has a relationship

nx>nz>=ny

which are refractive indexes of the film 3402.

As for the polarizing plates 3401 and 3404, the thickness of the entirepolarizing plate shall be 100 microns or more. On the other hand, thein-plane retardation (nx−ny)×d of the film is set to 40 nm or more to140 nm or less.

The retardation when a liquid crystal layer 3403 is vertically alignedshall be defined by

RLC=(n//−n⊥)×d.

When the sum of the negative retardation of the protective films for thepolarizing plates 3401 and 3404, the negative retardation of the film3402 having in-plane retardation, and the negative retardation ofanother layer having negative retardation is

Rnegatotal, the following relationship is set:

20 nm<RLC−Rnegatotal<150 nm.

This makes it possible to achieve a contrast 10 or more at an inclinedangle of ±70 degrees or more in all directions.

The in-plane retardation of the film 3402 having in-plane retardationserves as a function of rotating the polarization direction of polarizedlight. The film having negative retardation in a direction perpendicularto the layer serves as a function of canceling the positive retardationof the liquid crystal layer 3403. A positive retardation which has notbeen completely cancelled

RLC−Rnegatotal

has a function of bringing the polarized light from linearly polarizedlight into elliptically polarized light and adjusting its ellipticity.Further it acts to change the rotation direction of polarization of theelliptically polarized light.

A norbornene-based resin film is stretched in one direction to realizethe film having the relationship

nx>nz>=ny

as refractive indexes of the film 3402.

The polarizing plates 3401 and 3404, the polarizing plates having alarge thickness, have been conventionally used, for which polarizingplates each having a protective film made of triacetylcellulose and athickness of 100 μm or more are used.

The retardation film 3402 and the liquid crystal layer 3403 aresandwiched between the pair of polarizing plates 3401 and 3404. Anabsorption axis 3411 of the polarizing plate 3401 and an optical axis3412 of the retardation film 3402 adjacent thereto are arranged to beperpendicular to each other. The absorption axis 3411 of the polarizingplate 3401 and an absorption axis 3414 of the polarizing plate 3404 areperpendicular to each other.

In FIG. 35, a configuration is employed in which a film 3503 having anin-plane retardation of 40 nm to 130 nm (preferably from 60 nm to 110nm) is used as a protective film for a. polarizing plate 3510. Thepolarizing plate 3510 is constituted by laminating a protective film3501, a polarizing layer 3502, and the retardation film and protectivefilm 3503. A liquid crystal layer 3504 is sandwiched between thepolarizing plates 3510 and 3505. The polarizing layer 3502, theretardation film and protective film 3503, the liquid crystal layer 3504and the polarizing plate 3505 correspond to the polarizing plate 3401,the retardation film 3402, the liquid crystal layer 3403 and thepolarizing plate 3404 in FIG. 34 respectively.

Since the retardation film 3503 also serves as the protective film forthe polarizing plate 3510, the number of films for use in totaldecreases, which enables reduced cost. The negative retardation of thisfilm is also adjusted to satisfy the above-described relationship ofretardation.

For example, a norbornene-based resin film is stretched in twodirections or more to realize the film having negative retardation.

FIG. 36 shows a generalized configuration, in which the polarizing plate3505 on the lower side in FIG. 35 is changed. In place of the polarizingplate 3505, a polarizing plate 3610 is used. The polarizing plate 3610is constituted by laminating a film 3601, a polarizing layer 3602 and aprotective film 3603. An absorption axis 3612 of the polarizing layer3602 is in the same direction as that of the absorption axis 3515 of thepolarizing plate 3505 in FIG. 35.

The film 3601 is also capable of having in-plane retardation. In thiscase, its optical axis is set perpendicular to the absorption axis 3612of the adjacent polarizing layer 3602. Further, it is also possible toset the in-plane retardation of the film 3601 to almost zero. It is alsopossible to use a film having only negative retardation without in-planeretardation.

According to this embodiment, in FIG. 34, liquid crystal molecules canbe vertically aligned in the liquid crystal layer 3403. The retardationfilm 3402, which is a retardation film having retardation in the plane,is provided such that its optical axis is perpendicular to theabsorption axis of the adjacent polarizing layer 3401, and has arelationship of refractive indexes nx>nz>=ny (where nx is a refractiveindex in a direction of the optical axis, ny is a refractive index in anin-plane direction perpendicular to nx, and nz is a refractive index ina direction perpendicular to the plane). The first polarizing plate 3401is provided with a protective film having a thickness of 100 microns ormore. The retardation film 3402 has an in-plane retardation (nx−ny)×d (dis a thickness) of 40 nm or more to 130 nm or less.

The liquid crystal layer 3403 has a retardation RLC=(n//−n⊥)×d (n// is arefractive index in the longitudinal direction of a liquid crystalmolecule, n⊥ is a refractive index in a direction perpendicular to thelongitudinal direction of the liquid crystal molecule, and d is athickness) when the liquid crystal molecules are vertically aligned. Theliquid crystal layer 3403 has a relationship 20 nm<RLC−Rnegatotal<150 nmwhere Rnegatotal is the sum of the negative retardation of theprotective film for the polarizing plate 3401, the negative retardationof the retardation film 3402 and a negative retardation of another layerhaving the negative retardation when it is added. The polarizing plate3401 includes a protective film made of triacetylcellulose,norbornene-based resin, or polycarbonate.

In FIG. 35, the polarizing plate 3510 includes the protective film 3503having in-plane retardation. The protective film 3503 is provided suchthat the optical axis thereof is perpendicular to the absorption axis ofthe polarizing layer 3502. The polarizing plate 3510 is configured suchthat the in-plane retardation (nx−ny)×d of the protective film 3503 (nxis a refractive index in a direction of the optical axis, ny is arefractive index in a in-plane direction perpendicular to nx, and d is athickness) is set to 40 nm or more to 130 nm or less and, in the case oftwo protective films, the sum of in-plane retardations of the two filmsis set to 40 nm or more to 130 nm or less.

The liquid crystal layer 3504 has a retardation RLC=(n//−n⊥)×d when theliquid crystal molecules are vertically aligned and a relationship 20nm<RLC−Rnegatotal<150 nm where Rnegatotal is the sum of the negativeretardation of the protective film 3503 and a negative retardation ofanother layer having negative retardation when it is added.

As described above, the use of this embodiment enables realization of aliquid crystal display which is bright and has a wide viewing angle.

Fifth Embodiment

In order to realize a wide viewing angle, in the MVA-mode liquid crystaldisplay device, liquid crystal molecules are vertically aligned when novoltage is applied thereto, and separately tilt in four directions infour regions respectively when a voltage is applied thereto. The visualangle characteristics in the respective regions are mixed, resulting ina wide viewing angle. In such a case, the boundary between alignmentregions turns black, which presents a problem that the displaybrightness of white is not high. Therefore, a technique of realizing abright display by limiting the number of division to two is considered.

FIG. 37 shows an example of the manner of alignment in the liquidcrystal display device divided in two. The TFT substrate is formed witha gate line 3701, a data line 3702, a Cs line 3703 and an ITO pixelelectrode 3704. As shown by thick arrows 3711 and 3712, alignment isdivided by the Cs line 3703 running in the middle of a pixel and thegate line 3701. The boundaries of the alignment are hidden behind thegate line 3701 and the Cs line 3703. Such a two-domain display has aproblem that its viewing angle is narrow compared with that of thefour-domain type. Particularly, coloring at an inclined visual angle isa problem.

FIG. 38A shows its direction and the like. An example is taken in whichliquid crystal molecules are aligned in a divided manner to tilt in thetop and bottom directions as shown by the arrows 3711 and 3712. Anabsorption axis 3811 of an analyzer (polarizing plate) and an absorptionaxis 3812 of a polarizer (polarizing plate) are provided, in directionsshown in FIG. 38A, perpendicular to each other. In this display, theliquid crystal molecules are vertically aligned where no voltage isapplied thereto with the display in black. On the other hand, when avoltage is applied, the liquid crystal molecules tilt in the top andbottom directions in FIG. 38A, which allows light to pass therethroughby the birefringence of the liquid crystal to produce a white display.

A case in which an observer 3801 observes this display from the verticaldirection is explained here. FIG. 38B is a cross-sectional view of FIG.38A when viewed from the horizontal direction. A length 3822 of a liquidcrystal molecule 3821 looks short when viewed by the observer 3801.Therefore, the actual birefringence of the liquid crystal decreases, itswhite display slightly darkens or becomes bluish to some extent.

On the other hand, a case in which an observer 3802 observes thisdisplay from the horizontal direction in FIG. 38A is explained. FIG. 38Cis a cross-sectional view of FIG. 38A when viewed from the verticaldirection. An optical path 3832 of the liquid crystal layer which theobserver 3802 views is longer than an optical path 3833 when an observerviews the liquid crystal layer from the front. In this case, thebirefringence of the liquid crystal itself does not change, but thebirefringence of the liquid crystal layer increases because of thelonger optical path. This presents a problem that the display turns fromwhite into yellowish.

It is an object of this embodiment of the invention to decrease thephenomenon of turning to bluish or yellowish. Though “technique of usinga cholesteric layer and a quarter wave layer in combination” is proposedin order to increase the brightness of a backlight, the coloring at aninclined visual angle is utilized to decrease the coloring of the liquidcrystal display at an inclined visual angle is the main point of thisembodiment.

As shown in FIG. 39, the liquid crystal molecule alignment directions3711 and 3712 are opposite to each other. An absorption axis 3901 of apolarizing plate with a cholesteric reflective layer laminated thereonand an absorption axis 3902 of an analyzer are perpendicular to eachother. An optical axis 3903 of a quarter wave retardation layer tilts 45degrees from the above-described absorption axes 3901 and 3902. Theoptical axis 3903 of the quarter wave layer adjacent to the cholestericlayer is set to be perpendicular to the alignment directions 3711 and3712 of the liquid crystal molecules.

As shown in FIG. 41A, in the liquid crystal display device, a backlight4101, a cholesteric layer 4102, a quarter wave plate 4103 and a liquidcrystal layer (including polarizing plates) 4104 are laminated in order.The cholesteric layer 4102 and the quarter wave plate 4103 adjacentthereto are explained. Of incident light from the backlight 4101, thecholesteric layer 4102 reflects a counterclockwise circularly polarizedlight 4122 to make it a counterclockwise circularly polarized light4123, and allows a clockwise circularly polarized light 4121 to pass asit is a clockwise circularly polarized light 4131. Then, thecounterclockwise circularly polarized light 4123 which has beenreflected by the cholesteric layer 4102 is reflected by a reflector ofthe backlight 4101 to be a clockwise circularly polarized light 4124, isincident again on the cholesteric layer 4102 and passes through it. Inother words, the cholesteric layer 4102 converts, in cooperation withthe backlight 4101, incident natural light into the clockwise circularlypolarized light 4131. The quarter wave plate 4103 has a function ofconverting the incident circularly polarized light into linearlypolarized light. The quarter wave plate is explained with reference toFIGS. 40A and 40B.

FIG. 40A shows a case in which an optical axis 4002 of a quarter waveplate 4001 points in a depth direction in FIG. 40A. The quarter waveplate 4001 allows circularly polarized lights 4012 and 4022 to beincident thereon and linearly polarized lights 4013 and 4023 to exittherefrom. An observer 4011 at the front receives the light 4013, and anobserver 4021 at an inclined angle receives the light 4023.

When the quarter wave plate 4001 is a uniaxial optical film, the light4023, which exits toward the observer 4021 at the inclined angle in adirection perpendicular to the optical axis 4002 of the quarter waveplate 4001, generally becomes yellowish. In this direction, the opticalpath length (from C to D in FIG. 40A) of the obliquely incidentcircularly polarized light 4022 is longer than the optical path length(from A to B in FIG. 40A) of the vertically incident circularlypolarized light 4021, which increases birefringence. This results inexcessive birefringence at an inclined visual angle to cause yellowishcoloring in a system which is adjusted to create white without coloringat the front. This phenomenon corresponds to that of FIG. 38B.

FIG. 40B shows a case in which an optical axis 4032 of a quarter waveplate 4031 points in the horizontal direction in FIG. 40B. The quarterwave plate 4031 allows circularly polarized lights 4042 and 4052 to beincident thereon and linearly polarized lights 4043 and 4053 to exittherefrom. An observer 4041 at the front receives the light 4043, and anobserver 4051 at an inclined angle receives the light 4053.

The light 4053, which obliquely exits in a direction parallel to theoptical axis 4032 of the quarter wave plate 4031, generally becomesbluish. In this direction, the anisotropy in refractive index itselfdecreases at an inclined visual angle, which decreases effects ofbirefringence though the optical path length increases. Therefore, thebirefringence is insufficient at the inclined visual angle, which causesbluish coloring. This phenomenon corresponds to that of FIG. 38C.

Considering the liquid crystal layer 4104 in FIG. 41A, the samedescription can apply thereto about coloring, when the direction inwhich the liquid crystal molecules are aligned is substituted for thedirection of the optical axis of the aforementioned quarter wave plate,“having half wavelength” for the retardation, and linearly polarizedlight passed through the polarizer for the incident light. In short, thephenomena in FIGS. 38B and 38C occur.

FIGS. 41A and 41B show the whole configuration of the liquid crystallayer (including the polarizing plates) 4104, the quarter wave plate4103, the cholesteric layer 4102 and the backlight 4101, which are setsuch that optical axes 4111 and 4151 of the quarter wave plate 4103 andoptical axes 4112 and 4152 of the liquid crystal molecule of the liquidcrystal layer are perpendicular to each other. FIG. 41A shows a casewhen the whole configuration is observed from the top direction or thebottom direction in FIG. 39, and FIG. 418 shows a case when the wholeconfiguration is observed from the top right direction or the top leftdirection.

FIG. 41A is first explained. An observer 4133 at the front receives alight 4132 which is a light 4131 after exiting through the quarter waveplate 4103 and the liquid crystal layer 4104. An observer 4143 at aninclined angle receives a light 4142 which is a light 4141 after exitingthrough the quarter wave plate 4103 and the liquid crystal layer 4104.The light 4142 passing through the quarter wave plate 4103 adjacent tothe cholesteric layer 4102 becomes yellowish by the effect of its longeroptical path length. This phenomenon corresponds to that of FIG. 40A.Then, this light 4142 passes through the liquid crystal layer 4104, andit becomes bluish because the actual birefringence of the liquid crystalbecomes smaller. This phenomenon corresponds to that of FIG. 38B. Thus,the influence of the quarter wave plate 4103 (yellowish) and theinfluence of the liquid crystal layer 4104 (bluish) are canceled outeach other, which realizes a display with almost no coloring.

FIG. 41B shows a case in which the whole configuration is observed froma direction different by 90 degrees from that of FIG. 41A. An observer4163 at the front receives a light 4162 which is a light 4161 afterexiting through the quarter wave plate 4103 and the liquid crystal layer4104. An observer 4173 at an inclined angle receives a light 4172 whichis a light 4171 after exiting through the quarter wave plate 4103 andthe liquid crystal layer 4104. The light 4172 passing through thequarter wave plate 4103 adjacent to the cholesteric layer 4102 becomesbluish because the actual birefringence of the quarter wave plate 4103becomes smaller. This phenomenon corresponds to that of FIG. 40B. Then,this light 4172 passes through the liquid crystal layer 4104, and itbecomes yellowish by the effect of its longer optical path length. Thisphenomenon corresponds to that of FIG. 38B. Thus, the influence of thequarter wave plate 4103 (yellowish) and the influence of the liquidcrystal layer 4104 (bluish) are canceled out each other, which realizesa display with almost no coloring.

As described above, the coloring by the liquid crystal layer 4104 andthe coloring by the quarter wave plate 4103 are canceled out each otherto realize an excellent display.

FIG. 37 is an alignment state when a typical two-domain alignment isperformed. The pixel area is set which is surrounded by the gate lines3701 and the data lines 3702. Each pixel is provided with the TFT. Theliquid crystal molecules are vertically aligned where no voltage isapplied thereto. The directions in which the liquid crystal moleculestilt with application of a voltage are controlled by applyingultraviolet light to the surface of an alignment film or by pre-tilt byrubbing the surface of the alignment film. The directions in which theliquid crystal molecules tilt are set to directions perpendicular to thegate lines 3701 such that they tilt in the formation of stretched armsviewed from the gate lines 3701.

FIG. 39 shows the alignment directions 3711 and 3712 and directions ofthe absorption axes 3901 and 3902 of the polarizing plates and theoptical axis 3903 of the quarter wave plate with respect to thisTFT-LCD. In FIGS. 41A and 41B, a film made by stretching a polycarbonatefilm is used as the quarter wave plate 4103. The value of birefringenceat a wavelength of 550 nm is set in a range of 137.5 nm±10 nm. A TACfilm is used as a substrate film of the cholesteric liquid crystal layer4102. The pitch of the cholesteric liquid crystal is set to include arange of reflecting visible light and further to include the infraredregion. This enables realization of characteristics without great changein reflection wavelength from the cholesteric liquid crystal layer 4102even at an inclined angle in an oblique direction. As for the twisteddirection, a clockwise twisted cholesteric layer is used for thecholesteric layer 4102. The cholesteric liquid crystal layer 4102 isformed by applying a cholesteric liquid crystal several times and dryingindividual layers at room temperature for cure.

Although FIG. 39 shows a plane view, the sectional configuration isexplained using FIGS. 41A and 41B. A side-edge type backlight is used asthe backlight 4101. This configuration is made by laminating thecholesteric liquid crystal layer 4102, the quarter wave plate 4103, thepolarizer 4104, the liquid crystal panel 4104 and the analyzer 4104 inorder viewed from the backlight 4101. The Δn×d of the liquid crystallayer is set in a range from 200 nm to 400 nm.

It is effective to provide a light scattering layer between the quarterwave plate 4103 and the liquid crystal substrate 4104. Thatconfiguration is shown in FIG. 42. On a cholesteric layer 4201, aquarter wave plate 4202 and a scattering layer 4203 are laminated. Thisscattering layer 4203 is realized by mixing a scattering material in anadhesive which adheres the quarter wave plate 4202 to the polarizingplate. A scattering layer having scattering property of a Haze value of40 or more is employed.

FIG. 43 shows the measured result of the visual angle characteristicswhen this embodiment is actually employed. The coloring in a whitedisplay was measured in all directions at intervals of 15 degrees fromthe front at an inclined angle of 70 degrees. A region 4301 indicatesred, a region 4302 yellow, a region 4303 green, a region 4304 blue, anda region of the center thereof white.

A graph shown by rhombuses shows a case of a vertical two-domain panel(indicated as “NORMAL” in FIG. 43) without using the cholesteric layer4102 and the quarter wave plate 4103, in which a phenomenon of yellowishcoloring is viewed. A graph shown by squares shows a case without ascattering layer shown in FIGS. 41A and 41B (indicated as “WITHOUTSCATTERING LAYER” in FIG. 43). A graph shown by triangles shows theliquid crystal panel employing the configuration having the scatteringlayer shown in FIG. 42 added thereto (indicated as “WITH SCATTERINGLAYER” in FIG. 43), in which the coloring could be reduced at any visualangle in any direction.

The above explanation is made about the case of the vertical alignmentwhere no voltage is applied, and an embodiment in which the invention isapplied to a horizontal alignment display is explained here. FIGS. 44Aand 44B show an example in which the invention is applied to an IPS(in-plane switching mode) liquid crystal display.

FIG. 44A is a cross-sectional view of the IPS-mode liquid crystaldisplay. A liquid crystal layer 4402 is provided between an oppositesubstrate 4401 and a TFT substrate 4403. The TFT substrate 4403 isformed with a common electrode 4412 and a drain electrode 4411 throughan insulating film 4413. The opposite substrate 4401 is not providedwith an electrode. When a voltage is applied to the drain electrode4411, an electric field occurs between the drain electrode 4411 and thecommon electrode (the ground potential).

FIG. 44B is a plane view of the TFT substrate 4403 of the liquid crystaldisplay in FIG. 44A. The TFT substrate is formed with a gate line 4421,a data line 4422, a drain electrode 4423 and a common electrode 4424. Aliquid crystal molecule 4432 is aligned in a clockwise direction of 15degrees from the direction in which the drain electrode 4423 extendswhere no voltage is applied thereto. An absorption axis 4442 of apolarizing plate on the light incident side (an absorption axis of apolarizer) is set to be perpendicular to the alignment direction of theliquid crystal molecule 4432 where no voltage is applied. The alignmentof a liquid crystal molecule 4431 tilts in a direction perpendicular tothe drain electrode 4423 with the application of a voltage. In FIG. 44B,the liquid crystal molecule 4431 is aligned in a clockwise direction of60 degrees during a white display. Here, an optical axis 4443 of aquarter wave plate is set in a direction which is almost perpendicularto the alignment direction of the liquid crystal molecule 4431 duringthe white display and forms an angle of 45 degrees with the absorptionaxis 4442 of the polarizer. An absorption axis 4441 of the analyzer isperpendicular to the absorption axis 4442 of the polarizer.

In such an IPS-mode display here, the alignment direction of the liquidcrystal molecules in the white display can not completely be determined.The arrangement in this case is set such that the direction of theoptical axis of the quarter wave plate is perpendicular, as much aspossible, to the direction which is considered that the liquid crystalmolecules are rotated thereto and aligned therein, and that the opticalaxis of the quarter wave plate and the absorption axis of the polarizerto form an angle of 45 degrees.

According to this embodiment, the backlight 4101 supplies light in FIGS.41A and 41B. The cholesteric liquid crystal layer 4102 and the quarterwave plate 4103 are sandwiched between the backlight 4101 and the liquidcrystal panel 4104. The alignment direction of the liquid crystalmolecule of the liquid crystal panel 4104 and the optical axis of thequarter wave plate 4103 are perpendicular to each other.

As shown in FIG. 39, in the liquid crystal panel, the liquid crystalmolecules are vertically aligned where no voltage is applied thereto,and separately tilt in the two directions 3711 and 3712 which differ 180degrees from each other by applying a voltage. Alternatively, the liquidcrystal molecules may be arranged to tilt in one direction by applying avoltage.

In FIG. 42, the scattering layer 4203 is formed between the quarter waveplate 4202 and the liquid crystal panel 4104 (FIGS. 41A and 41B). Thescattering layer 4203 has a Haze value of 40 or more.

In FIGS. 44A and 44B, the liquid crystal molecule 4431 in the liquidcrystal panel is horizontally aligned where a voltage is appliedthereto, and the alignment direction is perpendicular to the opticalaxis 4443 of the quarter wave plate. It should be noted that the liquidcrystal molecule in the liquid crystal panel may be horizontally alignedwhere no voltage is applied thereto, and the alignment direction may beperpendicular to the optical axis of the quarter wave plate. The displaymode of the liquid crystal panel is the in-plane switching mode.

As described above, the use of this embodiment enables realization of abright display and a liquid crystal display with a wide viewing angle.

Sixth Embodiment

FIGS. 45A and 45B show an example of the electrode structure of theMVA-mode liquid crystal panel. FIG. 45A shows a case of four domains,and FIG. 45B shows a case of two domains. The MVA-mode liquid crystalpanel is provided with a domain control means, which is constituted byany of or a combination of a projection, a depression, and a slitprovided in electrodes 4510 and 4540, on a surface of at least one of apair of substrates. The MVA-mode liquid crystal panel uses a nematicliquid crystal having negative dielectric anisotropy, in which liquidcrystal molecules are aligned almost perpendicular to the substrate whenno voltage is applied thereto. The liquid crystal molecules arecontrolled by the domain control means so that the liquid crystalmolecules tilt in a plurality of directions in each pixel when a voltageis applied. On both sides of the liquid crystal panel, a pair ofpolarizing elements are disposed such that absorption axes 4501 and 4502(absorption axes 4531 and 4532) thereof are perpendicular to each other.

In the case of the fine slit electrodes 4510 and 4540 having a pitch ofabout 6 μm (line/space: 3 μm/3 μm), the liquid crystal molecules have aproperty of tilting in a direction parallel to the slits when a voltageis applied thereto.

Accordingly, when the slit electrode 4510 is formed so that liquidcrystal molecules 4521 to 4524 tilt in four directions as shown in FIG.45A, the alignment of four domains 4511 to 4514 is realized.Alternatively, when the slit electrode 4540 is formed so that liquidcrystal molecules 4551 and 4552 tilt in two directions as shown in FIG.45B, the alignment of two domains 4541 and 4542 is realized.

Next, the relationship between the tilt direction of the liquid crystalmolecule and the direction of the absorption axis of the polarizingelement is explained with FIGS. 46A to 46D. As shown in FIG. 46A, whenthe voltage is turned off, a liquid crystal molecule 4602 is alignedperpendicular to the substrate surface. FIG. 46A shows the relationshipbetween the liquid crystal molecule 4602 and absorption axes 4601 and4603 of the pair of polarizing elements in this event. The light passedthrough one of the polarizing elements passes through the liquid crystalwithout receiving influence of the birefringence of the liquid crystalmolecule 4602, and then is intercepted by the other polarizing element,resulting in a black display.

When the voltage is turned on as shown in FIGS. 46B and 46C, the liquidcrystal molecule having negative dielectric anisotropy tilts withrespect to the substrate surface, and when a sufficiently large voltageis applied, liquid crystal molecules 4.612 and 4622 become almostparallel to the substrate surface. In order to realize an optimal whitedisplay, the direction in which the liquid crystal molecule tilts issubjected to constraints with respect to the absorption axis.

FIG. 46B shows a case in which the liquid crystal molecule 4612 tilts ina direction parallel or perpendicular to an absorption axis 4613 whenthe voltage is turned on. In this case, the light passed through one ofthe polarizing elements passes through the liquid crystal withoutreceiving influence of the birefringence of the liquid crystal molecule4612, and then is intercepted by the other polarizing element as in thecase of the voltage being turned off. Therefore, it is impossible toobtain a white display.

In order to obtain an optimal white display, the tilt direction of theliquid crystal molecule 4622 should form angles of 45 degrees withabsorption axes 4621 and 4623 as shown in FIG. 46C. In this case, thelinearly polarized light passed through one of the polarizing elementsis brought into elliptically polarized light by receiving the influenceof the birefringence of the liquid crystal molecule 4622 to create lightwhich passes through the other polarizing element, resulting in a whitedisplay.

Therefore, as shown in FIG. 46D, the four directions in which liquidcrystal molecules 4641 to 4644 should tilt when a voltage is appliedthereto, in the MVA-mode liquid crystal panel, are limited to thedirections which form angles of 45 degrees with absorption axes 4631 and4632.

In the MVA-mode liquid crystal panel having regions arranged in a mixedmanner in one pixel, in which the liquid crystal molecules tilt indifferent directions when a voltage is applied thereto, it is desirablethat the liquid crystal molecules tilt only in the four directions shownin FIG. 46D. Actually, however, some liquid crystal molecules tilt indirections other than the four directions shown in FIG. 46D.

An MVA-mode liquid crystal panel having an electrode 4710 with fourdomains 4711 to 4714 shown in FIG. 47 is explained as an example. Liquidcrystal molecules 4721 to 4724 tilt in different four directions by afine slit electrode 4710 which is formed to form angles of 45 degreeswith absorption axes 4701 and 4702 of a pair of polarizing elements. Atboundary regions where the regions are adjacent to each other, however,liquid crystal molecules 4725 to 4728 are forced to tilt in directionsparallel or perpendicular to the absorption axes 4701 and 4702.

Light does not pass through the regions where the liquid crystalmolecules 4725 to 4728 tilt in directions parallel or perpendicular tothe absorption axes 4701 and 4702. Therefore, in the electrode structureshown in FIG. 47, a black region in the shape of a cross appears in awhite display, which causes the transmittance to greatly decrease.

In this embodiment of the invention, the directions of the domaincontrol means periodically disposed at fine pitches in the MVA-modeliquid crystal panel include the directions to form angles of 45 degreeswith the absorption axes of the polarizing elements and anotherdirection.

As has been described by now, in the MVA-mode liquid crystal panel, whenthe liquid crystal molecule tilts in a direction other than thedirections to form angles of 45 degrees with the absorption axes of thepolarizing elements, the region does not transmit light, which is acause of decrease in the transmittance. Means for solving this problemis explained hereafter.

A first means is the addition of a chiral material to a liquid crystalmaterial. The addition of the chiral material allows the liquid crystalmolecule to tilt while twisting from one substrate to the othersubstrate when a voltage is applied thereto. This utilizes the similarprinciple to that of the horizontally aligned liquid crystal panel whichis generally called TN mode. Therefore, the twisted angle of the liquidcrystal molecules is desirably about 90 degrees.

In other words, it is desirable that d/p=¼, and, at least, it should besatisfied that ⅛≦d/p≦⅜, where the cell gap of the liquid crystal panelis d, and the helical pitch of the chiral material is p.

A second means is, as shown in FIG. 48, the arrangement of a pair ofquarter wave plates 4802 and 4804 on both sides of a liquid crystalpanel 4803, and further arrangement of a pair of polarizing elements4801 and 4805 on both sides thereof. Retardation axes 4812 and 4814 ofthe quarter wave plates 4802 and 4804 and absorption axes 4811 and 4815of the adjacent polarizing elements 4801 and 4805 form angles of 45degrees respectively. The arrangement is made such that the retardationaxes 4812 and 4814 of the quarter wave plates 4802 and 4804 areperpendicular to each other, and the absorption axes 4811 and 4815 ofthe polarizing elements 4801 and 4805 are perpendicular to each other.

The light passed through the polarizing element becomes linearlypolarized light, and then passes through the quarter wave plate to becircularly polarized light. In this event, the intensity of the passedlight does not depend on the tilt direction of the liquid crystalmolecule but is determined only by the retardation of a liquid crystalcell.

FIGS. 49A to 49C show examples of the pattern of the periodicallydisposed domain control means (ITO pixel electrode). As shown in FIG.49A, pixel electrodes 4901 which are the domain control means aredisposed in an almost radial pattern, which makes it possible to changethe tilt directions of the liquid crystal molecules from almost 0degrees to 360 degrees sequentially.

Similarly, it is possible to realize various variations of pattern suchas a pattern of pixel electrodes 4902 in which the liquid crystalmolecules tilt in eight directions as shown in FIG. 49B, or a pattern ofconcentric pixel electrodes 4903 as shown in FIG. 49C. The pixelelectrodes 4901 to 4903 in FIGS. 49A to 49C are one connected pixelelectrode respectively.

As described above, the liquid crystal panel is structured such that thedirections of the domain control means periodically disposed at finepitches include the directions to form angles of 45 degrees with theabsorption axes of the polarizing elements and other directions, andadded with the chiral material or is combined with the ¼ plates, so thata wide viewing angle and high brightness can be realized at the sametime.

This embodiment is explained more specifically. An overall electrode isformed over the entire surface of the display region on one of the pairof substrates constituting the liquid crystal panel. On the othersubstrate, pixel electrodes are formed. The pixel electrode, as shown inFIG. 49A, is composed of the fine slit electrodes 4901 in a radialpattern. Further, on the substrate, a color filter, gate bus lines, databus lines, TFT devices and the like are formed.

Vertical alignment films are formed on both substrates. Both thesubstrates are bonded together through spacers, and a nematic liquidcrystal having negative dielectric anisotropy, which is added with achiral material to have a relationship d/p=¼, is sealed therebetween toproduce a liquid crystal panel. On both sides of the liquid crystalpanel, polarizing elements are arranged in such a manner that theabsorption axes thereof are perpendicular to each other.

Another configuration example is explained. An overall electrode isformed over the entire surface of the display region on one of the pairof substrates constituting the liquid crystal panel. On the othersubstrate, pixel electrodes are formed. The pixel electrode, as shown inFIG. 49A, is composed of the fine slit electrodes 4901 in a radialpattern. Further, on the substrate, a color filter, gate bus lines, databus lines, TFT devices and the like are formed.

Vertical alignment films are formed on both substrates. Both thesubstrates are bonded together through spacers, and a nematic liquidcrystal having negative dielectric anisotropy is sealed therebetween toproduce a liquid crystal panel.

On both sides of the liquid crystal panel, polarizing elements arearranged in such a manner that the absorption axes thereof areperpendicular to each other. A quarter wave plate is disposed betweenthe liquid crystal panel and each of the polarizing elements such thatthe retardation axis of the quarter wave plate and the absorption axisof the adjacent polarizing element form an angle of 45 degrees, and theretardation axes of the quarter wave plates are perpendicular to eachother.

According to this embodiment, as shown in FIG. 48, the liquid crystalpanel 4803 has the liquid crystal sealed between the pair of substrates.The pair of polarizing elements 4801 and 4805 are arranged on both sidesof the liquid crystal panel 4803 such that the absorption axes thereofare perpendicular to each other. The domain control means are providedon the surface of at least one of the pair of substrates constitutingthe liquid crystal panel 4803. The domain control means include aperiodical pattern of any of or a combination of a projection such as aprotrusion, a depression, or a slit provided in the electrode (FIG. 47)to control the alignment of the liquid crystal molecules in the liquidcrystal panel.

As shown in FIG. 47, the alignment directions of the liquid crystalmolecules 4721 to 4728 by the domain control means include the fourdirections to form angles of 45 degrees with the absorption axes 4701and 4702 of the polarizing elements and other directions. In the liquidcrystal panel, the liquid crystal molecules are almost verticallyaligned with respect to the substrates when no voltage is appliedthereto and are controlled by the domain control means to tilt in aplurality of directions in each pixel when a voltage is applied thereto.

As shown in FIGS. 49A to 49C, the liquid crystal panel may include aregion where the alignment directions of the liquid crystal molecules bythe domain control means sequentially change, a region where theysequentially change from 0 degrees to 360 degrees. In FIG. 49A, theliquid crystal panel includes a region where the domain control meansare arranged in a radial pattern, in which the width of the domaincontrol means increases as it goes outward from the center of the radialpattern. In FIG. 49C, the liquid crystal panel includes a region wherethe domain control means are concentrically arranged.

The liquid crystal panel is added with the chiral material in its liquidcrystal material. The condition ⅛≦d/p≦⅜ is satisfied, where the cell gapof the liquid crystal panel is d and the helical pitch of the chiralmaterial is p.

As shown in FIG. 48, the pair of quarter wave plates 4802 and 4804 areprovided between the pair of polarizing elements 4801 and 4805 in such amanner to interpose the liquid crystal panel 4803 therebetween. Theretardation axes of the pair of quarter wave plates 4802 and 4804 andthe absorption axes of the pair of polarizing elements 4801 and 4805adjacent thereto form angles of 45 degrees respectively, and theretardation axes of the pair of quarter wave plates 4802 and 4804 areperpendicular to each other.

As described above, according to this embodiment, it becomes possible torealize a liquid crystal display device with a wide viewing angle andhigh brightness.

Seventh Embodiment

The MVA alignment control technique includes the followings.

(1) Alignment Control by a Protrusion or a Slit

FIGS. 50A and 50B show the alignment control by the protrusion. A liquidcrystal layer 5002 is provided between an opposite substrate 5001 and aTFT substrate 5003. The opposite substrate 5001 is provided with atransparent electrode 5012 and a protrusion 5011. The TFT substrate 5003is provided with a transparent electrode 5016 and a protrusion 5015. Asshown in FIG. 50A, liquid crystal molecules 5013 near the protrusions5011 and 5015 tilt in accordance with the shapes of the protrusions 5011and 5015 where no voltage is applied thereto. A liquid crystal molecule5014 which is distant from the protrusions 5011 and 5015 is verticallyaligned. As shown in FIG. 50B, electric fields 5021 are formed inaccordance with the shapes of the protrusions 5011 and 5015 where avoltage is applied. A force is exerted on a liquid crystal molecule 5022to align it in a direction perpendicular to the electric field 5021.Thus, the alignment of the liquid crystal molecules can be controlled bythe protrusion 5011 and 5015.

FIGS. 50C and 50D show the alignment control by the electrode slit. Aliquid crystal layer 5032 is provided between an opposite substrate 5031and a TFT substrate 5033. The opposite substrate 5031 is provided with atransparent electrode 5041. The TFT substrate 5033 is provided with atransparent electrode 5042 having a slit. As shown in FIG. 50C, a liquidcrystal molecule 5043 is vertically aligned with respect to thesubstrates where no voltage is applied thereto. As shown in FIG. 50D, anoblique electric field 5051 occurs by the slit of the transparentelectrode 5042 where a voltage is applied. A force is exerted on aliquid crystal molecule 5052 to align it in a direction perpendicular tothe electric field 5051. Thus, the alignment of the liquid crystalmolecule can be controlled by the electrode 5042 in a slit form. Itshould be noted that the motion of the liquid crystal molecules near theprotrusion and near there are the same as those in FIG. 50B, and thusthe illustration thereof is omitted.

(2) Alignment Control by an Auxiliary Protrusion or an Auxiliary Slit

FIG. 51A shows the alignment control by the auxiliary protrusion. Apixel electrode 5101 is provided on the TFT substrate, and a protrusion5102 is provided on the opposite substrate. Further, an auxiliaryprotrusion 5103 is provided on the opposite substrate corresponding toan edge part of the pixel electrode 5101. It is possible to match thealignment directions of the liquid crystal molecules 5104 between theprotrusion 5102 and the auxiliary protrusion 5103. If there is noauxiliary protrusion 5103, the alignment of liquid crystal molecules5122 controlled by the protrusion 5102 and the alignment of liquidcrystal molecules 5121 controlled by the electric field at the edge partof the pixel electrode 5101 compete with each other as shown in FIG.51C.

FIG. 51B shows the alignment control by the auxiliary slit. A pixelelectrode 5113 is provided with a slit 5111. Further, auxiliary slits5112 are provided near an edge part of the pixel electrode 5113. It ispossible to prevent competition of the alignment by the edge part of thepixel electrode 5113 and the alignment by the slit 5111 to match thealignment directions of the liquid crystal molecules.

(3) Alignment Control by a Fine Pattern (Protrusions or Slits)

FIG. 52A shows the alignment control by the fine slits. A pixelelectrode 5201 has fine slits. An electric field 5202 is formed inaccordance with the shape of the silts. A liquid crystal molecule 5203is aligned in accordance with the electric field 5202. As shown in FIG.52B, a slit 5212 is provided between pixel electrodes 5211 and 5213, andfurther a protrusion 5214 is provided. The alignment direction of aliquid crystal molecule 5221 when a voltage is applied is controlled byan electric field occurring near the slit 5212 of the pixel electrode5213. The alignment of a liquid crystal molecule 5223 is controlled bythe protrusion 5214. If the fine slits in FIG. 52A are formed in thepixel electrode 5213, the alignment of a liquid crystal molecule 5222between the liquid crystal molecules 5221 and 5223 can also becontrolled.

(4) Alignment Control by a Pattern in the Shape of Paddy Field

FIG. 53 shows the alignment control by the pattern in the shape of paddyfield (cross shape). A pixel electrode 5303 is provided on the TFTsubstrate. Protrusions 5301 and 5302 in a cross shape are provided onthe opposite substrate. The protrusions 5301 and 5302 forms four regionsto align in different directions liquid crystal molecules 5311 to 5314in each region.

The above described alignment controls (1) to (4) have respectivecharacteristics, and thus it is desirable to appropriately use them inaccordance with application. However, it is necessary to arrange manyprotrusions and slits, for example, in the control by (1), or some slitsmight exist just inside the pixel edge as in the top left and the bottomleft corner part of the pixel electrode 1404 in the layout in FIG. 14.Because the pixel edge is equivalent to the slit, controls by the pixeledge and the slits are adjacent to influence on each other at the topleft and the bottom left corner part. An unstable domain occurs at thepixel corner, which decreases the brightness.

It is difficult to completely control the alignment of the entire regionin the pixel by the control of only one kind of controls (1) to (4).Especially, this problem becomes serious in realizing:

-   a) high brightness (increase in transmittance)-   b) high definition-   c) fast response.

A combination of the control means of (1) to (4) suitable for importantparts of the pixel in a compound manner is more effective than separateperformance of the control means.

FIG. 54 shows a first configuration example. A pixel electrode isprovided in correspondence with a data line 5401 and a gate line 5402.First, fine slits 5416 are laid out at pixel corner parts to facilitatethe layout at the corner parts. In FIG. 54, it is just needed to lay outtwo linear protrusions 5411 and 5417 in the pixel and extend the fineslits 5416 therefrom toward the pixel corners. This results in not onlyeasy layout but also no formation of unstable domain to increase thetransmittance. The alignment is controlled by, in addition to the above,a slit 5412, fine slits 5415, auxiliary slits 5414 and auxiliaryprotrusions 5413. It should be noted that the protrusions and theauxiliary protrusions are formed on the opposite substrate, and the dataline, the gate line, the pixel electrode and the electrode slits areprovided on the TFT substrate.

With this configuration, the transmittance can be improved by 10% to 20%as compared to that by the technique (1) by itself. In the pixel, thereare a part where the alignment direction of the liquid crystal ispreferably changed in a range of 90 degrees or less and a part where itis preferably changed in a range of 90 degrees to 180 degrees. Forexample, the control by the protrusion of (1) is a control meanssuitable for changing the alignment direction by 180 degrees, but whenthe control is applied to the part where 90-degree change is required,it is difficult to perform an ideal control.

The alignment control (1) is applicable to 180 degrees,

-   the alignment controls (2) and (4) are applicable to 90 degrees, and-   the alignment control (3) is applicable to either above angle    depending on its own angle.

FIG. 54 is explained in more detail. The fine slits 5416 are extended tothe top right and the bottom right corner of the pixel to fit them tothe shapes of the corners. The fine slits 5415 of (3) are provided in adirection perpendicular to the main slit 5412 to enhance thecontrollability. Further, the fine slits 5415 at the pixel edge part arepartially made deep to make them (2) the auxiliary fine slits 5414 toprevent occurrence of an abnormal domain. Of course, (1) the protrusions5411 and 5417, which are the base of MVA are provided, that is, thetechniques of (1) to (3) are laid out at appropriate parts. Thetransmittance thereof is improved to be 1.15 times as compared to thecontrol only by (1) the protrusion and the slit which are the base ofMVA.

FIG. 55 shows a second configuration example. The TFT substrate isprovided with a data line 5501, a gate line 5502, a pixel electrode 5512and auxiliary fine electrode slits 5513. The opposite substrate isprovided with protrusions 5511. In the second configuration example, thetechnique of (3) is more positively used as compared to the firstconfiguration example, in which the fine slits 5513 are provided tomatch the shapes of pixel corners and a part where the alignmentdirection changes 90 degrees at the pixel center. The number of domainsin this case is only four, which can suppress loss in transmittance atan alignment divided part to a minimum. The transmittance furtherimproves to be 1.09 times as compares to the first configurationexample.

FIG. 56 shows a third configuration example. The TFT substrate isprovided with the data line 5501, the gate line 5502, a pixel electrode5612 and auxiliary fine electrode slits 5613. The opposite substrate isprovided with protrusions 5611. The number of domains of the thirdconfiguration example is also four that is the same as in the secondconfiguration example. The third configuration example basicallyresembles the second configuration example, but differs therefrom inthat the protrusion 5611 is disposed in the letter T (controls (2) and(4)) and that a main slit 5614 is obliquely provided at the pixelcenter. The third configuration example includes all of the controlmethods of (1) to (4). The transmittance improves 1.12 times as comparedto the first configuration example.

FIG. 57 shows a fourth configuration example. The TFT substrate isprovided with the data line 5501 and the gate line 5502, a pixelelectrode 5712 and auxiliary fine electrode slits 5713. The oppositesubstrate is provided with a protrusion 5711. The fourth configurationexample resembles the third configuration example but differs therefromin the manner of disposing the protrusion 5711. The transmittanceimproves by about 10% as compared to that of the first configurationexample.

FIG. 58 to FIG. 60 show fifth configuration examples. In FIG. 58, theTFT substrate is provided with the data line 5501, the gate line 5502, apixel electrode 5811 and a contact region 5812. In FIG. 59, the TFTsubstrate is provided with the data line 5501, the gate line 5502, apixel electrode 5911 and a contact region 5912, and the oppositesubstrate is provided with a protrusion 5913. In FIG. 60, the TFTsubstrate is provided with the data line 5501, the gate line 5502, apixel electrode 6011 and a contact region 6012, and the oppositesubstrate is provided with a protrusion 6013. In each of the fifthconfiguration examples, the fine electrodes join together in such amanner that they are connected together by a cross pattern at the centerof the pixel. Any of the configuration examples has a layout made bycombining the controls (2) to (4) in a complex manner. The transmittanceimproves by about 20% as compared to that of the first configurationexample.

FIG. 61 and FIG. 62 show sixth configuration examples. In FIG. 61, theTFT substrate is provided with the data line 5501, the gate line 5502and a pixel electrode 6111, and the opposite substrate is provided withprotrusions 6112. In FIG. 62, the TFT substrate is provided with thedata line 5501, the gate line 5502 and a pixel electrode 6211, and theopposite substrate is provided with protrusions 6212. The sixthconfiguration examples are similar to the fifth configuration examples,but differ therefrom in the method of connecting the fine electrodes inwhich they are connected by a linear pattern at the center of the pixel.The transmittance improves by about 20% , as in the fifth configurationexamples, as compared to that of the first configuration example. Eachof the second to sixth configuration examples, which has four domains,is more advantageous when it is applied to a higher definition case.

FIG. 63 to FIG. 66 show seventh configuration examples. In FIG. 63, theTFT substrate is provided with the data line 5501, the gate line 5502and a pixel electrode 6311, and the opposite substrate is provided witha protrusion 6312. In FIG. 64, the TFT substrate is provided with thedata line 5501, the gate line 5502 a pixel electrode 6411, and theopposite substrate is provided with a protrusion 6412. In FIG. 65, theTFT substrate is provided with the data line 5501, the gate line 5502and a pixel electrode 6511. FIG. 66, the TFT substrate is provided withthe data line 5501, the gate line 5502 and a pixel electrode 6611, andthe opposite substrate is provided with a protrusion 6612. Each of theseventh configuration examples has six divided domains. The seventhconfiguration examples are suitable for a relatively large pixel (whichdoes not mean that the second to sixth configuration examples can notapply to a large pixel). This is because, if a large pixel is divided bya small division number, one divided region has a large area, resultingin a larger region to be covered by one control element. Thetransmittance in the seventh configuration examples also improves byabout 10% as compared to that of the first configuration example.

FIG. 67 and FIG. 68 show eighth configuration examples. In FIG. 67, theTFT substrate is provided with the data line 5501, the gate line 5502, apixel electrode 6711 and fine slits 6712, and the opposite substrate isprovided with protrusions 6713. In FIG. 68, the TFT substrate isprovided with the data line 5501, the gate line 5502, a pixel electrode6811 and protrusions 6813, and the opposite substrate is provided with aprotrusion 6812. The eighth configuration examples have six domains,which are improved versions of the first configuration example. Thetransmittance becomes higher than that of the first configurationexample inversely to the area of the protrusion existing in the pixelwhich is smaller than that of the first configuration example. Thetransmittance improves by about 5% as compared to that of the firstconfiguration example.

A ninth configuration example adopts a slightly different idea from thatof the other configuration examples. Although FIG. 67 is a view showingonly one pixel, in the ninth configuration example, a pixel adjacent tothis pixel is laid out in a manner horizontally reversed (the adjacentpixels are not necessarily reversed, but pixels in close vicinity shouldbe reversed). Two pixels are brought into one set to obtain domains infour directions. The transmittance improves by about 10% as compared tothat of the first configuration example.

FIG. 69 shows a tenth configuration example. A protrusion 6901 isprovided on the opposite substrate (upper substrate), and a protrusion6902 is provided on the TFT substrate (lower substrate). At a regionwhere the alignment direction is changed 90 degrees, the protrusionpatterns on the upper and lower substrates are interchanged. This allowsthe directions of liquid crystal molecules to be changed without anydifficulty, resulting in stable alignment. As a result of applying thispattern to the center of the pixel of the first configuration example,the transmittance improves by about 0.5%.

The above-described configuration examples are to be considered asillustrative, and the above-described improvement in transmittance canbe expected by basically combining the controls (1) to (4) atappropriate parts (improper combination naturally decreases effect).Further, it is, of course, possible to further stable the alignmentusing a polymerization method of polymerizing monomers blended in theliquid crystal, thereby increasing the response speed. Moreover, it ispossible to further enhance the transmittance by combining with aquarter wave plate.

According to this embodiment, as shown in FIG. 50A, the surfaces of thetwo substrates 5001 and 5003 have been subjected to vertical alignmentprocessing, so that the liquid crystal layer 5002 is vertically alignedwhere no voltage is applied thereto. As shown in FIG. 50B, the liquidcrystal layer 5002 is a negative type liquid crystal layer sandwichedbetween the substrates, in which liquid crystal molecules point in adirection perpendicular to the electric fields 5021 caused byapplication of voltage. The domain control means conducts control suchthat the liquid crystal molecules tilt in directions of a plurality ofliquid crystal domains in each pixel, and includes first and seconddomain control means. The first domain control means is provided in apart of the pixel or a peripheral region thereof to vary the alignmentdirection of the liquid crystal in a range of 90 degrees to 180 degreesacross the center of the partially provided domain control means. Thesecond domain control means varies the alignment direction of the liquidcrystal in a range of 0 degrees to 90 degrees. The first and seconddomain control means preferably control the liquid crystal domain tohave 4 to 12 domains which are formed in the pixel.

The first domain control means is composed of any of or a combination ofsome of: the dielectric projection (protrusion) 5214 extending in adirection differing from the direction of the liquid crystal domain by45 degrees to 90 degrees (FIG. 52B); the electrode slits 5213 and 5212extending in the direction differing from the direction of the liquidcrystal domain by 45 degrees to 90 degrees (FIG. 52B); the electrodeslits 5201 elongated in the direction of the liquid crystal domain andperiodically repeated in the direction differing from the direction ofthe liquid crystal domain by 45 degrees to 90 degrees (FIG. 52A); andthe dielectric projections elongated in the direction of the liquidcrystal domain and periodically repeated in the direction differing fromthe direction of the liquid crystal domain by 45 degrees to 90 degrees.

The second domain control means is the dielectric projections(protrusions) 5301 and 5302 extending in a direction differing from thedirection of the liquid crystal domain by 0 degrees to 45 degrees (FIG.53), or the electrode slit extending in a direction differing from thedirection of the liquid crystal domain by 45 degrees.

The present embodiments are to be considered in all respects asillustrative and no restrictive, and all changes which come within themeaning and range of equivalency of the claims are therefore intended tobe embraced therein. The invention may be embodied in other specificforms without departing from the spirit or essential characteristicsthereof.

As described above, the proportions of a region where liquid crystalmolecules tilt in a direction of 0 degrees to 180 degrees and a regionwhere liquid crystal molecules tilt in a direction of 180 degrees to 360degrees are made different to be appropriate proportions, which makes itpossible to perform a suitable display even if a screen is viewed fromthe top or the bottom direction.

Further, the shape of a pixel electrode is formed in accordance with ofa gate line and a data line, which allows the alignment directions ofthe liquid crystal molecules by the pixel electrode to match thealignment directions of the liquid crystal molecules by the gate lineand the data line.

Furthermore, a half wave plate is provided between a pair of polarizinglayers, which enables realization of a liquid crystal display devicewith a wide viewing angle and high brightness.

Moreover, a predetermined retardation film is provided between first andsecond polarizing plates, which enables realization of a liquid crystaldisplay device with a wide viewing angle and high brightness.

Further, the alignment direction of the liquid crystal molecule of aliquid crystal panel and the optical axis of a quarter wave plate arearranged perpendicular to each other, which can prevent coloring of thedisplay screen even if it is viewed at an incline angle.

Further, by virtue of a domain control means, the alignment directionsof the liquid crystal molecules include directions to form angles of 45degrees with the absorption axes of polarizing elements and otherdirections, which enables a display with high brightness.

Further, both first and second domain control means are provided, whichimproves controllability of the alignment of the liquid crystal in theentire pixel.

1. A liquid crystal display device, comprising: a first substrate and asecond substrate; a liquid crystal layer sandwiched between said firstand second substrates, in which liquid crystal molecules are verticallyaligned with respect to said first and second substrates in a statewhere no voltage is applied between said first and second substrates; athin film transistor provided on said first substrate and including agate, a source, and a drain, a gate line connected to the gate of saidthin film transistor; a data line connected to the source of said thinfilm transistor; a pixel electrode in a comb or a slit shape connectedto the drain of said thin film transistor, directions of comb teeth orslit thereof, with the right direction on a screen being 0 degrees,extending in four directions of 45 degrees, 135 degrees, 225 degrees and315 degrees; and a color filter layer formed on said first substrate. 2.The liquid crystal display device according to claim 1, wherein saidpixel electrode has a width of 10 μm or less and a gap of μm or less. 3.The liquid crystal display device according to claim 2, wherein thewidth of said pixel electrode is set to 3 μm or more to 5 μm or less,and the gap of said pixel electrode is set to 2 μm or more to 5 μm orless.
 4. The liquid crystal display device according to claim 1, whereinsaid first and second substrates interposing said liquid crystal layertherebetween are sandwiched between a pair of polarizers and aretardation film which is provided between said first or secondsubstrate and one of the pair of polarizers, and said retardation filmhas in-plane retardation set to 40 nm or more than 130 nm or less. 5.The liquid crystal display device according to claim 1, wherein saidfirst and second substrates interposing said liquid crystal layertherebetween are sandwiched between a pair of polarizers and tworetardation films which are separately provided between said first andsecond substrate and the pair of polarizers, and the sum of in-planeretardations of said two retardation films is set to 40 nm or more to140 nm or less.
 6. The liquid crystal display device according to claim5, wherein an optical axis of said retardation film is perpendicular toan absorption axis of the adjacent polarizer.
 7. The liquid crystaldisplay device according to claim 1, wherein said first and secondsubstrates interposing said liquid crystal layer therebetween aresandwiched between a pair of quarter wave plates being perpendicular toeach other.
 8. The liquid crystal display device according to claim 1,wherein said first substrate has a subsidiary capacitor formingelectrode line extending in the horizontal direction at the middle ofthe pixel, and said pixel electrode is formed vertically divided withsaid subsidiary capacitor forming electrode line as a boundary, andsuperposed on said subsidiary capacitor forming electrode line near saidsubsidiary capacitor forming electrode line.